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TDA7541B
AM/FM car radio tuner IC w stereo decoder and intelligent selectivity system
TDA7541BAM/FM car radio tuner IC with stereo decoder
and intelligent selectivity system
Features FM part AGC generation by RF and IF detection I/Q mixer for 1st IF 10.7 MHz with image
rejection
–Mixer for 2nd IF 450 kHz Internal 450 kHz band pass filter with
bandwidth control by ISS Fully integrated FM demodulator with noise
cancellation AM part Wide and narrow AGC generation
–Mixer for 1st IF 10.7 MHz, AM up
conversion
–Mixer for 2nd IF 450 kHz Integrated AM-demodulator AM IF noise blanking Stereo decoder PLL with adjustment free, fully integrated
VCO Automatic pilot dependent
MONO/STEREO switching Programmable ROLL-OFF compensation High cut and stereo blend-characteristics
programmable Dedicated RDS mute Audio noise blanker Additional features VCO for world tuning range High performance fast PLL for RDS-
System IF counter for FM and AM with search stop
signal Quality detector for level, deviation,
adjacent channel and multipath ISS (Intelligent selectivity system) for
cancellation of adjacent channel and noise
influences Adjacent channel mute Fully electronic alignment Independent weather band input All functions I2 C bus controlled
DescriptionThe TDA7541B is a high performance tuner
circuit with stereo decoder for AM/FM car radio. It
contains a mixer, IF amplifier, demodulator for AM
and FM, stereo decoder, quality detection, ISS
filter and PLL synthesizer with IF counter on a
single chip. Use of BICMOS technology allows the
implementation of several tuning functions and a
minimum of external components.
Table 1. Device summary
Contents TDA7541B
Contents Block circuit diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Pin connection and pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Electrical specifications and characteristics . . . . . . . . . . . . . . . . . . . . 103.1 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3.1 Globals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3.2 FM section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3.3 AM section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.3.4 Stereo decoder section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.3.5 PLL section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264.1 FM part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.1.1 Mixer 1 AGC and IF amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.1.2 Mixer2, limiter, FM demodulator and spike cancellation . . . . . . . . . . . . 26
4.1.3 Quality detection and ISS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.1.4 Block diagram quality detection principle . . . . . . . . . . . . . . . . . . . . . . . . 29
4.1.5 Strong adjacent channel correction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.1.6 Weak signal mute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.1.7 Weather band input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2 AM section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2.1 Usage of control bit ADSEL (Addr23D7) . . . . . . . . . . . . . . . . . . . . . . . . 32
4.3 Stereo decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.3.1 Decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.3.2 Noise blanker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3.3 Functional description of the multipath detector . . . . . . . . . . . . . . . . . . 37
4.3.4 Quality detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.3.5 AFS control and stereo decoder mute . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.4 PLL and IF counter section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
TDA7541B Contents4.4.1 PLL frequency synthesizer block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.4.2 IF counter block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.5 I2 C bus interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Software specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.1 Chip address and overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.2 Address organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.3 Control register function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.4 Data byte specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
List of tables TDA7541B
List of tables
Table 1. Device summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Table 2. Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table 3. Thermal data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Table 4. Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Table 5. Globals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Table 6. FM section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Table 7. AM section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Table 8. Stereo decoder section. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 9. PLL section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Table 10. ISS filter control by I2 C bus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Table 11. Internal ISS control signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Table 12. ISS control modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Table 13. Usage of ADSEL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Table 14. Address organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Table 15. I2 C control bit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Table 16. Subaddress description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Table 17. Addr 0 TPLL charge pump control (0Bh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Table 18. Addr 1 TPLL Counter 1 (LSB). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Table 19. Addr 2 TPLL Counter 2 (MSB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Table 20. Addr 3 TV(00h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Table 21. Addr 4 TV/IF Counter (FM ACh, AM 1Ch) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Table 22. Addr 5 TPLL Divider (FM 3Dh, AM 2Dh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Table 23. Addr 6 AGC (FM 06h, AM 2Ah) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Table 24. Addr 7 Quality AC (FM 50h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Table 25. Addr 8 Quality ACM/MP (FM 6Ah) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Table 26. Addr 9 Quality Dev (FM 49h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Table 27. Addr 10 Quality MUX/FSU (FM 0Eh, AM 0Fh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Table 28. Addr 11 Weak Signal Mute (FM A8h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Table 29. Addr 12 AM IF NB (AM B1h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Table 30. Addr 13 XTAL adjust(80h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Table 31. Addr 14 IF2 adjust (FM E8h, AM 08h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Table 32. Addr 15 IQ adjust / Switch (FM E7h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Table 33. Addr 16 FM keying AGC (FM 1Dh). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Table 34. Addr 17 Roll off / Level gain (77h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Table 35. Addr 18 SD Stereoblend / AM corner frequency (0Dh) . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Table 36. Addr 19 SD High cut (2Fh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Table 37. Addr 20 SD MP (FM 97h, AM 3Fh). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Table 38. Addr 21 SD Quality (FFM 7Ah, AM FAh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Table 39. Addr 22 SD NB I (FM 05h, AM 04h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Table 40. Addr 23 SD NB II (FM E2h, AM C2h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Table 41. Addr 24, 26, 27, 28, 29 testing (FEh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Table 42. Addr 25 Testing (FEh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Table 43. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
TDA7541B List of figures
List of figures
Figure 1. Block circuit diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 2. Pin connection (top view) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 3. Programming of HC filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Figure 4. Programming of stereo blend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 5. Adaptive threshold control of noise blanker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Figure 6. Stereo blend controlled threshold adjust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Figure 7. Deviation controlled threshold adjust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Figure 8. Block diagram FM part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Figure 9. Block diagram VCO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Figure 10. Block diagram ISS function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Figure 11. Block diagram AM path. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Figure 12. Block diagram stereo decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Figure 13. Block diagram audio noise blanker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Figure 14. Block diagram multi path detection for stereo decoder. . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Figure 15. Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Figure 16. LQFP64 mechanical data and package dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Block circuit diagram TDA7541B Block circuit diagram
Figure 1. Block circuit diagram
TDA7541B Pin connection and pin description Pin connection and pin description
2.1 Pin connection
Figure 2. Pin connection (top view)
Pin connection and pin description TDA7541B
2.2 Pin description
Table 2. Pin description
TDA7541B Pin connection and pin description
Table 2. Pin description (continued)
Electrical specifications and characteristics TDA7541B Electrical specifications and characteristics
3.1 Thermal data
3.2 Absolute maximum ratings
3.3 Electrical characteristics
3.3.1 Globals
Tamb = 25 °C, VCC1 = VCC2 = VCCMIX1 = VCCVCO = VCCIF = 8.5 V, fXtal = 10.25 MHz,
in application circuit, unless otherwise specified.
Table 3. Thermal data
Table 4. Absolute maximum ratings
Table 5. Globals
TDA7541B Electrical specifications and characteristics
3.3.2 FM section
Tamb = 25 °C, VCC1 = VCC2 = VCCMIX1 = VCCVCO = VCCIF = 8.5 V, fXtal = 10.25 MHz,
fRF = 98 MHz, dev = 40 kHz, fMod = 1 kHz, in application circuit, unless otherwise specified.
Table 5. Globals (continued)
Table 6. FM section
Electrical specifications and characteristics TDA7541B
Table 6. FM section (continued)
TDA7541B Electrical specifications and characteristics
Table 6. FM section (continued)
Electrical specifications and characteristics TDA7541B
Table 6. FM section (continued)
TDA7541B Electrical specifications and characteristics
Table 6. FM section (continued)
Electrical specifications and characteristics TDA7541B
Table 6. FM section (continued)
TDA7541B Electrical specifications and characteristics
3.3.3 AM section
Tamb = 25 °C, VCC1 = VCC2 = VCCMIX1 = VCCVCO = VCCIF = 8.5 V, fXtal = 10.25 MHz,
fRF = 1 MHz, m = 30%, fmod = 1 kHz, in application circuit, unless otherwise specified.
Table 7. AM section
Electrical specifications and characteristics TDA7541B
Table 7. AM section (continued)
TDA7541B Electrical specifications and characteristics
3.3.4 Stereo decoder section amb = 25 °C, V CC1 = V CC2 = V CCMIX1 = V CCVCO = V CCIF = 8.5 V, fXtal = 10.25 MHz, MPX = 500 mVrms mono, f = 1 kHz, de-emphasis = 50 µs, in application circuit, unless
otherwise specified.
Can be reached in application circuit, not measured.
Table 7. AM section (continued)
Table 8. Stereo decoder section
Electrical specifications and characteristics TDA7541B
Table 8. Stereo decoder section (continued)
TDA7541B Electrical specifications and characteristics
Table 8. Stereo decoder section (continued)
Electrical specifications and characteristics TDA7541B
Table 8. Stereo decoder section (continued)
TDA7541B Electrical specifications and characteristics Intermodulation suppression
measured with: 91 % stereo signal; 9 % pilot signal; fm = 10 kHz or 13 kHz. Traffic radio (V.F.) suppression
measured with: 91% stereo signal; 9% pilot signal; fm=1 kHz; 5% sub carrier (f=57 kHz, fm=23 Hz AM, m=60 %) SCA (subsidiary communications authorization)
measured with: 81 % mono signal; 9 % pilot signal; fm=1 kHz; 10 % SCA - sub carrier (fS = 67 kHz, unmodulated) ACI (adjacent channel interference)
measured with: 90 % mono signal; 9 % pilot signal; fm=1 kHz; 1% spurious signal (fS = 110 kHz or 186 kHz, unmodulated) All thresholds are measured in test mode at the quality output. The thresholds are calculated by VNBTH - VPEAK. VPEAK can
be adjusted by applying a 150 kHz sinewave at MPXIN.
Table 8. Stereo decoder section (continued)
Electrical specifications and characteristics TDA7541B
3.3.5 PLL section
Tamb = 25 °C, VCC1 = VCC2 = VCCMIX1 = VCCVCO = VCCIF = 8.5 V, fXtal = 10.25 MHz,
VMPX = 500 mVrms mono, f = 1 kHz, de-emphasis = 50 µs, in application circuit, unless
otherwise specified.
Table 9. PLL section
TDA7541B Electrical specifications and characteristics
Table 9. PLL section (continued)
Functional description TDA7541B
4 Functional description
4.1 FM part
4.1.1 Mixer 1 AGC and IF amplifier
FM quadrate I/Q-mixer converts FM RF to IF1 of 10.7 MHz. The mixer provides inherent
image rejection and wide dynamic range with low noise and large input signal performance.
For accurate image rejection the phase-error of I/Q can be compensated by software (PH).
It is capable of tuning the US FM, US weather (dedicated WB input), Europe FM, Japan FM
and East Europe FM bands: US FM = 87.9 to 107.9 MHz US weather = 162.4 to 162.55 MHz Europe FM = 87.5 to 108 MHz Japan FM = 76 to 91 MHz East Europe FM = 65.8 to 74 MHz
The AGC operates on different sensitivities and bandwidths in order to improve the input
sensitivity and dynamic range. AGC thresholds are programmable by software (RFAGC,
IFAGC, and KAGC). The output signal is a controlled current for pin diode attenuator.
A 10.7 MHz programmable amplifier (IFG) correct the IF ceramic insertion loss and the
costumer level plan application.
4.1.2 Mixer2, limiter, FM demodulator and spike cancellation
In the 2nd mixer stage the first 10.7 MHz IF is converted into the second 450 kHz IF.
The fully integrated sample and hold FM demodulator including spike cancellation (DSB)
converts the IF signal from the 450 kHz limiter (limiter gain 80 dB typ.) to the FM multiplex
output signal with very low distortion.
The sensitivity of spike blanking can be set via I2 C bus.
4.1.3 Quality detection and ISS
Field strength
Parallel to mixer2 input a 10.7 MHz limiter generates a signal for digital IF counter and field
strength voltage VFSUint. This internal voltage VFSUint is used for AM IF noise blanker,
adjacent channel and multi path detection and is available at PIN27 (FSU) in a range of 0 V
to 5 V. The offset and slope of FSU signal can be adjusted via I2 C bus (FSWO and SL) for
application adaptation.
The voltage VFSWO including offset adjust is externally filtered at PIN37 (FSWO) and used
for weak signal mute function and generation of ISS filter control signals in weak signal
condition. It is possible to combine the IF counter result with this voltage VFSWO by
programmable comparator threshold (SSTH).
TDA7541B Functional description
Adjacent channel detector
The input of the adjacent channel detector is AC coupled from VFSW. A programmable
high-pass or band-pass (ACF) as well as rectifier generate a signal which is compared with
adjustable threshold (ACTH). The output signals of this comparator is controlling the charge
and discharge of the external capacitor at PIN30 or PIN31 (dependent on SEEK) with
programmable discharge current (TISS). The level at PIN30/31 is used to generate the two
digital signal ac and ac+ for ISS control. The adjacent channel information behind the
rectifier is available as analog output signal at the multiplexer output (PIN23).
Multipath detector
The input of the multi path detector is AC coupled from internal VFSW too. After filtering with
19 kHz band-pass and rectifying, this voltage is compared with an adjustable threshold
(MPTH). The output signal of this comparator can be used to switch off the adjacent channel
detection. This influence is selectable by I2 C bus (MPENA).
The multi path information behind the rectifier is available as analog output signal at
multiplexer output (PIN23).
450 kHz IF narrow band pass filter (ISS filter)
The device has an additional 450 kHz IF narrow band-pass filter for suppression of noise
and adjacent channel signal influences. This narrow filter has three switchable bandwidths,
narrow range of 80 kHz, mid range of 120 kHz and 22 kHz for weather band information.
Without ISS (Intelligent Selectivity System) filter the IF bandwidth (wide range) is defined
only by ceramic filter chain and mixer2 bandwidth. The filter is located between mixer2
output buffer and 450 kHz limiter stage. The centre frequency is matched to the
demodulator centre frequency.
Deviation detector
In order to avoid distortion in audio output signal the narrow ISS filter is switched OFF if over
deviation is present. Hence the demodulator output signal is detected. After AC coupling,
low-pass filtering and peak rectifying this signal is charging/discharging the external DEVTC
capacitor by an IIC programmable charge/discharge current (TDEV). The voltage at DEVTC
is compared with adjustable thresholds (DWTH, DTH) and generates two digital control
signals (dev, dev+). For weak signal condition the deviation threshold depends on FSWO.
ISS switch logic
All digital control signals coming from adjacent channel detector, deviation detector and
weak signal mute are acting via switching matrix on ISS filter switch. IF2 narrow band-pass
switch mode is controlled also by software (ISSENA, ISSON, WBON, ISSBW, and BWDEF).
The switching of the IF band-pass is also possible to influence by external manipulation of
DC voltage at PIN30.
The influence of the ISS software control on the functionality of the ISS filter is described in
Table 10. The value “X” for the control bit means the bit does not influence the filter control in
this condition.
Functional description TDA7541B
Description of I2 C bits:
ISSENA
ISS filter enable
“1”: ISS filter control enabled
“0”: ISS filter is switched off (bypass of the filter, wide)
ISSON
ISS filter control mode
“1”: ISS filter is in manual control mode (switched "ON"); the bits ISSBW and WBON are
defining the bandwidth
“0”: ISS filter is in automatic control mode according to mode1/2 table
ISSBW
ISS filter band width
“1”: 80 kHz
Table 10. ISS filter control by I2 C bus
TDA7541B Functional description
“0”: 120 kHz
The bit has only influence if bit BWENA is “1”, or if bit ISSON is “1”
WBON
Weather band enable
“1”: Weather band enable (FMmixer1 is disabled, Wbmixer1enabled, stereo decoder gain
26dB, ISS filter bandwidth 22 kHz, IF2Q=”00”)
“0”: Weather band disable
For weather band enable it is need to set ISSON = “1”
ISSM
ISS filter application mode
“0”: ISS filter application mode1
“1”: ISS filter application mode2
If BWENA is “1” the band width is always switched to ISSBW in case of ISS filter activated
BWDEF
Enable bit ISSBW for ISS filter band with control
“1”: ISS filter is internally controlled, but band width is defined by bit ISSBW
“0”: ISS filter is internally controlled, band width is defined by mode1/2 table
For the internal control two application modes are available (ISSM). The conditions and
settings are described in Table 11 and Table 12.
4.1.4 Block diagram quality detection principle
(without overdeviation correction)
Table 11. Internal ISS control signals
Functional description TDA7541B
4.1.5 Strong adjacent channel correction
Under strong adjacent channel it is possible to have disturbance of the audio signal created
by interference between ISS filter control (deviation detection) and adjacent channel mute.
The control bits SACCE and SACCT can be used to avoid this disturbance. If the function is
activated (SACCE = “1”) the IF counter together with the internal field strength is used to
suppress a malfunction of deviation detection. The bit SACCT is changing the sensitivity of
the SACC block (SACCT = “1” means higher sensitivity).
Figure 10 shows the ISS block diagram including the SACC function.
Note: The IF counter must be switched ON if this function is used (Addr25D4 = “1”)
4.1.6 Weak signal mute
The filtered field strength signal (FSWO) is the reference for soft slope mute control in weak
signal condition to eliminate audible effects. The start point and mute depth are
programmable (WMTH, WMD) in a wide range. These settings together with FSWO bits are
influencing the weak signal mute behavior. The time constant is defined by external
capacitance at PIN 42. Additional adjacent channel mute function is supported. A high pass
filter with -3 dB threshold frequency of 100 kHz, amplifier and peak rectifier generates an
adjacent noise signal from Demodulator output. This value is compared with adjustable
threshold (ACMTH). For present strong adjacent channel the MPX signal is additional
attenuated (ACMD) and has the same time constant as weak signal mute.
Table 12. ISS control modes
TDA7541B Functional description
4.1.7 Weather band input
If the weather band input is used the chip must be set in FM mode (FMON). In addition to
that the ISS filter must be switched ON (ISSENA=”1”), mixer2 quality factor must be set to
IF2Q=”00” and the ISS filter must be set in manual control mode (ISSON=”1”).
The bit WBON is: activating the WB input switching the ISS filter in WB mode (22 kHz band width) switching the stereo decoder InGain to 26 dB.
In order to increase the selectivity in weather band mode the AM 450kHz ceramic filter can
be used in series to the ISS filter by activating ADSEL (please refer to Figure 10, ISS block
diagram and Section 4.2.1, usage of bit ADSEL).
4.2 AM section
signals, narrow band information (DAGC) referred to PIN 56, up conversion signal (IFAGC)
at PIN 61 and wide band information (RFAGC) at PIN 3.This gain control gives two output
signals. The first one is a current for pin diode attenuator and the second one is a voltage for
preamplifier. Time constant of RF and IF-AGC is defined by internal 100 k resistor and
external capacitor at PIN 54. The intervention points for AGC (DAGC, IFAGC and RFAGC)
are programmable by software. The oscillator frequency for upconversion-mixer1 is
generated by dividing the VCO frequency after VCO divider (VCOD) and AM pre-divider
(AMD).
Two 10.7 MHz ceramic filters before mixer2 input increase 900 kHz attenuation.
The AMIF2 block contains mixer2, IF2 amplifier, demodulator and AGC2 The AM/FM mixer2
converts 10.7 MHz IF1 into 450 kHz IF2. Mixer2 output passes a 450 kHz narrow band filter
(LC plus ceramic filter). LC centre frequency is adjustable by I2 C bus (IF2A). The following
IF2 amplifier provides signal for fully integrated demodulator. If the bit ADSEL is activated,
the ISS filter is inserted between IF2 amplifier and demodulator in order to increase the
selectivity (please refer to Figure 11, AM path block diagram and Section 4.2.1, usage of bit
ADSEL).
Mixer2 and IF2 amplifier have a 2-stage AGC with careful take-over behavior to keep
distortion low. The IF2 AGC range is about 55 dB.
The input signal of IF2 amplifier is used in limiter circuit for in-band level detection. The
electrical characteristics are described in FM section.
The demodulator is a peak detector to generate the audio output signal.
At the MUX output the AMIF stereo is available.
AM IF noise blanker
In order to remove in AM short spikes a noise cancellation conception is used in 450 kHz IF
AM level. The advantage is to avoid long narrow AGC- and demodulator- time constants,
which enlarge spike influences on audio signal and makes difficult to remove it in audio path.
The 10.7 MHz AM IF signal behind IF1 amplifier generates via limitation an unweighted field
strength signal including slope of noise spike. The comparison of this detected slope
between fast and slow rectifier ignores audio modulation whereby the threshold of slow
Functional description TDA7541B
rectifier is programmable (AINBT). A comparator activates a pulse generator. The duration
of this pulse is software programmable (AINT) and is smooth blanking out the spikes in mixer2.
4.2.1 Usage of control bit ADSEL (Addr23D7)
The control bit ADSEL can be used to increase the selectivity of the application in AM mode
and WB mode. In FM it has no function. Table 12 shows the functionality of the control bit.
4.3 Stereo decoder
4.3.1 Decoder
The stereo decoder-part of the TDA7541B contains all functions necessary to demodulate
the MPX-signal, like pilot tone-dependent MONO/STEREO switching as well as the stereo
blend and high cut.
Adaptations like programmable input gain, roll-off compensation, selectable de-emphasis
time constant and a programmable field strength input allow easy adoption to different
applications.
The 4th order input filter has a corner frequency of 80 kHz and is used to attenuate spikes
and noise and acts as an anti-aliasing filter for the following switch capacitor filters.
Demodulator
In the demodulator block the left and the right channel are separated from the MPX-signal.
In this stage also the 19 kHz pilot tone is canceled. For reaching a high channel separation
the TDA7541B offers an I2 C bus programmable roll-off adjustment, which is able to
compensate the low pass behavior of the tuner section. Within the compensation range an
adjustment to obtain about 40 dB channel separation is possible. The bits for this
adjustment are located together with the level gain adjustment in one byte. This gives the
Table 13. Usage of ADSEL
TDA7541B Functional description
possibility to perform an optimization step during the production of the car radio where the
channel separation and the field strength control are trimmed.
In addition to that the FM signal can be inverted.
De-emphasis and high cut
The de-emphasis low pass allows to choose between a time constant of 50 µs/75 µs
(DEEMP). The high cut control range will be in both cases THC = 2 x TDeemp. Inside the high
cut control range (between VHCHT and VHCLT) the LEVEL signal is converted into a 5-bit
word, which controls the low pass time constant between TDeemp...3 x TDeemp. Thereby the
resolution will remain 5 bits referred to the voltage range between the VHCHT - and minimum
VHCLT -values.
The high cut function can be switched off by I2 C-bus.
Figure 3. Programming of HC filter
In AM mode (FMON = 0) the DEEMP bit together with the AM corner frequency bits (AMCF)
can be used as programmable AM frequency response. The maximum corner frequency is
defined by TDeemp, the minimum is defined by 3 x TDeemp For the over all frequency
response it is need to take into account the frequency response of the AF output at
MPXOUT and the Stereo decoder demodulator too.
19 kHz PLL and pilot tone detector
The PLL has the task to lock on the 19 kHz pilot tone during a stereo-transmission to allow a
correct demodulation. The included pilot tone-detector enables the demodulation if the pilot
tone reaches the selected pilot tone threshold VPTHST. Two different thresholds are
available. The status of the detector output can be checked by reading the status byte of the
TDA7541B via I2 C bus or by reading the STEREO status at MUX pin23.
Field strength control
The field strength input is used to control the high cut- and the stereo blend-function. In
addition the signal can be also used to control the noise blanker thresholds and as input for
the multipath detector.
Functional description TDA7541B
10k between FSU pin and FSTC pin. The second stage is a programmable gain stage to
adapt the VFSTC signal internally. The gain (LG) is widely programmable in 16 steps from dB to 8.25 dB (step=0.55dB). These 4 bits are located together with the Roll-Off
compensation bits in byte 14 to simplify a possible adaptation during the production of the car radio.
Stereo blend control
The stereo blend control block converts the internal LEVEL-voltage into a demodulator
compatible analog signal, which is used to control the channel separation between 0dB and
the maximum separation. Internally this control range has a fixed upper limit, which is the
internal reference voltage VREF1. The lower limit can be programmed between 29 and % of VREF1 in 4 % steps. In order to adjust the external voltage VFSTC to the internal
control range two values must be defined: the Level gain LG and VSBL. Full channel
separation is reached when the internal level voltage (VST) becomes bigger than VREF1.
Therefore the following equation can be used to estimate the gain:
The MONO-voltage VMO (0dB channel separation) can be chosen selecting SBC.
Figure 4. Programming of stereo blend
High cut control
The high cut control set-up is similar to the stereo blend control set-up: the starting point
VHCH can be set with 2 bits to be 42, 50, 58 or 66 % of VREF1 whereas the range can be
set to be 11, 18.3, 25.7 or 33 % of VHCH.
4.3.2 Noise blanker
In the automotive environment spikes produced for example by the ignition or the wiper-
motor disturb the MPX-signal. The aim of the noise blanker part is to cancel the audible
influence of the spikes. Therefore the output of the stereo decoder is held at the actual
voltage for a time between 22 ms and 38 ms (programmable).
In a first stage the spikes must be detected but to avoid a wrong triggering on high
frequency (white) noise a complex trigger control is implemented. Behind the trigger stage a
pulse former generates the "blanking"-pulse. An own biasing circuit supplies the noise
blanker in order to avoid any cross talk to the signal path.
TDA7541B Functional description
Trigger path
The incoming FM demodulator output signal is taken in front of the weak signal mute, high
pass filtered, amplified and rectified. This second order high pass filter has a corner-
frequency of 140 kHz. The rectified signal, VRECT, is low pass filtered to generate a signal
called VPEAK. Noise with a frequency above 140 kHz increases the VPEAK voltage. The
resulting voltage can be adjusted by use of the noise rectifier discharge current. The VPEAK
voltage is fed to a threshold generator, which adds to the VPEAK voltage a DC threshold
VTH. Both signals, VRECT and VPEAK+VTH are fed to a comparator, which triggers a re-
triggerable monoflop. The output of the monoflop activates the sample-and-hold circuit in
the signal path for the selected duration.
Automatic noise controlled threshold adjustment
There are mainly two independent possibilities for programming the trigger threshold:
1. Low threshold in 8 steps (NBLT)
2. Noise adjusted threshold in 4 steps (NBCT).
The low threshold is active in combination with a good MPX signal without any noise; the
VPEAK voltage is less than 1V. The sensitivity in this operation is high.
If the MPX signal is noisy (low field strength) the VPEAK voltage increases due to the higher
noise, which is also rectified. With increasing of the VPEAK voltage the trigger threshold
increases, too. This particular gain is programmable in 4 steps (NBCT).
Figure 5. Adaptive threshold control of noise blanker
Automatic stereo blend controlled threshold adjustment
Besides the noise controlled threshold adjustment there is an additional possibility for
influencing the noise blanker trigger threshold using the bits NBFC. This influence depends
on the stereo blend control. The point where the MPX signal starts to become noisy is fixed
by the RF part. This point is also the starting point of the normal noise-controlled trigger
adjustment. But in some cases the noise blanker can create a wrong triggering, which
create distortion, already in the region of mono/stereo transition. Therefore an opportunity to PEAK voltage by the stereo blend function it is implemented.
Functional description TDA7541B
Figure 6. Stereo blend controlled threshold adjust
Automatic deviation controlled threshold adjustment
If the system is tuned to stations with a high deviation the noise blanker can trigger on the
higher frequencies of the modulation. To avoid this wrong behavior, which causes noise in
the output signal, the noise blanker offers a deviation-dependent threshold adjustment. By
rectifying the MPX signal a further signal representing the actual deviation is obtained. It is
used to increase the PEAK voltage. The gain of this circuit is programmable in 3 steps
(NBDC) of the stereo decoder-byte (the first step turns off the detector).
Figure 7. Deviation controlled threshold adjust
Multipath influence on noise blanker
To react on high repetitive spikes caused by a Multipath-situation, the discharge-time of the PEAK voltage can be decreased depending on the voltage-level at Pin MPTC. There are
two ways to do this.
a) Switch on the linear influence of the Multipath-Level on the PEAK-signal. In this
case the discharge slew rate is 1 V/ms. The slew rate is measured with R Discharge
= infinite and VMPTC = 2.5 V
b) Activate a function, which switches to the 18k discharge resistor if the Multipath-
Level is below 2.5 V . If multipath influence on noise blanker is switched ON than
MPF bit has to be set to 0.
TDA7541B Functional description
Noise blanker in AM mode
In AM mode the noise blanker is activated if a spike on the audio signal is bigger than a fixed
threshold. In order to blank the whole spike in AM mode the hold time of the S&H circuit is
much longer than in FM mode (64 0µs -1,2 ms). It is not recommended to use the AM noise
blanker without to use the AMIF noise blanker inside the tuner.
4.3.3 Functional description of the multipath detector
Using the internal multi path detector the audible effects of a multi path condition can be
minimized. A multi path condition is detected by rectifying the 19 kHz spectrum in the field
strength signal. An external capacitor is used to define the attack- and decay-times. The
MPTC pin is used as detector output connected to a capacitor. Using this configuration an
external adaptation to the user's requirement is possible without affecting the "normal" field
strength input (FSTC) for the stereo decoder.
To keep the old value of the multi path detector during an alternative frequency jump, the
MPFAST bit can disconnect the external capacitor.
Selecting MPINT the channel separation is automatically reduced during a multipath
condition according to the voltage appearing at the MPTC pin.
To obtain a good multipath performance an adaptation is necessary. Therefore the gain of
the 19 kHz band pass is programmable in four steps (MPG) and the rectifier gain is
programmable in four steps (MPRG). The attack- and decay-times can be set by the
external capacitor value and the multipath detector charge current MPCC.
4.3.4 Quality detector
The TDA7541B offers a quality detector output, which gives a voltage representing the FM-
reception conditions. To calculate this voltage the MPX-noise and the multipath-detector
output are summed according to the following formula:
The VPEAK signal is described in noise blanker session. The factor 'a' can be programmed
from 0.6 to 1.05 (QDC) and the factor b can be programmed from 6 dB to 15 dB (QNG). The
quality output voltage can be read at the MUX pin. The MUX pin is a low impedance output
and is able to drive external circuitry as well as simply fed to an AD-converter for RDS
applications.
4.3.5 AFS control and stereo decoder mute
In case of AFS (alternative frequency search) jump it is recommended to set the stereo
decoder in mute condition (SDM) and in addition to set the SEEK mode. Since these two
bits are placed in the first written byte, this can be done in the same write cycle as the PLL
jump. The stereo decoder mute is high impedance mute, which means the charge on the
coupling capacitor will be kept. Simultaneously the pilot detector circuit of the stereo
decoder is switched into hold mode. The SEEK mode is switching the multi path detector
into fast mode. The external capacitor at MPTC is disconnected from multipath detector
which keeps the stereo blend condition, but makes the quality information in fast mode
available at the MUX pin.
Functional description TDA7541B
4.4 PLL and IF counter section
4.4.1 PLL frequency synthesizer block
This part contains a frequency synthesizer and a loop filter for radio tuning system. Only one
VCO is required to build a complete PLL system for FM world tuning and AM up conversion.
VCO and dividers
The varactor tuned LC oscillator together with the dividers provides the local oscillator signal
for both AM and FM front-end mixers. The VCO has an operating frequency of
approximately 160 MHz to 260 MHz. In FM mode the VCO frequency is divided (VCOD) by
1, 2 or 3. These dividers generate in-phase and quadrature-phase output signals using in
FM mixer for image rejection.
In AM mode the divided VCO frequency is additional pre-divided (AMD) by 4, 6, 8 or 10
dependent on selected AM band.
PLL frequency generation for phase comparison
The VCO divided signals applies a two modulus counter (32/33), which is controlled by a 5-
bit A-divider. The 5-bit register (PC0 to PC4) controls this divider. In parallel the output of the
swallow counter is connected to an 11-bit B-divider. The 11-bit PC register (PC5 to PC15)
controls this divider. Dividing range behind VCO divider:
Warning: For correct operation: A 32; B A
Crystal oscillator
The crystal oscillator provides 10.25 MHz signal for conversion from IF1 to IF2 as well as
switching signals for ISS- and quality detection filter. Furthermore reference dividers
generate from adjustable crystal frequency (XTAL) reference frequencies for the tuning PLL,
IF counter and FM demodulator.
The various reference frequencies f REF of PLL (RC) can be chosen by IIC-bus.
Three state phase comparator
The phase comparator generates a phase error signal according to phase difference
between f SYN and f REF . This phase error signal drives the charge pump current generator.
Charge pump current generator
This system generator signed pulses of current. The phase error signal decides the duration
and polarity of those pulses. The current absolute values are programmable by register ICP.
In lock detector
After reaching a phase difference about lower than 40 ns the inlock detector is automatically
switching the charge-pump in low current mode (LDENA).
TDA7541B Functional description
Low noise CMOS op-amp
An internal voltage divider at pin 19 connects the positive input of the low noise op-amp. The
charge pump output connects the negative input. This internal amplifier in cooperation with
external components can provide an active filter. The negative input is switchable to two
input pins, to increase the flexibility in application. While the high current mode is activated
LPHC output is switched on.
Antenna DAC
For tuning of FM antenna tank circuit two different modes are available (TVM). One is the
auto-alignment measurement of VCO tuning voltage with offset of 8-bit DAC (TVO). The
other one is an adjustment of 8-bit DAC independent on PLL tracking. For big differences
between VCO tuning voltage and antenna tank control voltage an additional constant offset
voltage can be switched to antenna circuit (TVO+).
4.4.2 IF counter block
The aim of IF counter is it to measure the intermediate frequency of the tuner. The input
signals are the output level of 10.7 MHz IF-limiter in FM and output level of 450 kHz IF-
limiter in AM.
The grade of integration is adjustable by different measuring cycle times (IFS). The
tolerance of the accepted count value is adjustable too (EW), to reach an optimum
compromise for search speed and precision of the evaluation.
Sampling timer
A sampling timer generates the gate signal for the main counter. The basically sampling
time are in FM 6.25 kHz (tTIM = 160 s) and in AM 1 kHz (tTIM = 1 ms). This is followed by an
asynchronous divider to generate several sampling times.
Intermediate frequency main counter
This counter is an 11 - 21-bit synchronous auto reload down counter. The counter length is
automatic adjusted to the chosen sampling time and the counter mode (FM or AM).
At the start the counter will be loaded with a defined value which is an equivalent to the
divider value (tSample x fIF).
If a correct frequency is applied to the IF counter frequency input at the end of the sampling
time the main counter is changing its state. This is detected by control logic and an external
search stop output is changing from LOW to HIGH.
The IF counter is started only by the in lock information from the PLL part.
4.5 I2 C bus interface
The TDA7541B supports the I2 C bus protocol. This protocol defines any device that sends
data onto the bus as a transmitter, and the receiving device as the receiver. The device that
controls the transfer is a master and device being controlled is the slave. The master will
always initiate data transfer and provide the clock to transmit or receive operations.
