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TDA1220B
AM-FM QUALITY RADIO
TDA1220BAM-FM QUALITY RADIO
The TDA1220B is a monolithic integrated circuit in
a 16-lead dual in-line package.
It is intended for quality receivers produced in large
quantities.
The functions incorporated are:
AM SECTION Preamplifier and double balanced mixer One pin local oscillator IF amplifier with internal AGC Detector and audio preamplifier
FM SECTION IF amplifier and limiter Quadrature detector Audio preamplifier
The TDA1220B is suitable up to 30MHz AM and for
FM bands (including 450KHz narrow band) and
features: Very constant characteristics (3V to 16V) High sensitivity and low noise Very low tweet
March 1993
BLOCK DIAGRAM Sensitivity regulation facility (*) High recovered audio signal suited for stereo
decoders and radio recorders Very simple DC switching of AM-FM Low current drain AFC facility
(*) Maximum AM sensitivity can be reduced by means of a resistor
(5 to 12KΩ) between pin 4 and ground.
1/18
THERMAL DATA
PIN CONNECTION(Top view)
ABSOLUTE MAXIMUM RATINGS
TDA1220B
AM SECTION (fo = 1 MHz; fm = KHz)
FM SECTION (fo = 10.8 MHz; fm = 1 KHz)
ELECTRICAL CHARACTERISTICS ( Tamb = 25 °C, Vs = 9V unless otherwise specified, refer to test circuit)
TDA1220B
Figure 1. Test circuit
Figure 2. PC board and component layout (1:1 scale) of the test circuit
TDA1220B
Figure 3. Audio output, noise
and tweet levels vs. input
signal (AM section)
Figure 4. Distortion vs. input
signal and modulation index
(AM section)
Figure 5. Audio output vs.
supply voltage (AM section)
Figure 6. Audio output and
noise level vs. input signal (FM
section)
Figure 7. Distortion vs. input
signal (FM section)
Figure 8. Audio output vs.
supply voltage (FM section)
Figure 9. Amplitude modu-
lation rejection vs. input signal
(FM section)
Figure 10. Δ DC output voltage
(pin. 9) vs. frequency shift (FM
section)
Figure 11. Δ DC output voltage
(pin 9) vs. ambient
temperature (FM section)
TDA1220B
APPLICATION INFORMATION
AM Section
RF Amplifier and mixer stagesThe RF amplifier stage (pin 2) is connected directly to the secondary winding of the ferrite rod antenna or
input tuned circuit. Bias is provided at pin 4 which must be adequately decoupled. The RF amplifier provides
stable performance extending beyond 30 MHz.
The Mixer employed is a double - balanced multiplier and the IF output at pin 3 is connected directly to the
IF filter coil.
Local oscillatorThe local oscillator is a cross coupled differential stage which oscillates at the frequency determined by the
load on pin 1.
The oscillator resonant circuit is transformer coupled to pin 1 to improve the Q factor and frequency stability.
The oscillator level at pin 1 is about 100 mV rms and the performance extends beyond 30 MHz, however
to enhance the stability and reduce to a minimum pulling effects of the AGC operation or supply voltage
variations, a high C/L ratio should be used above 10 MHz.
An external oscillator can be injected at pin 1. The level should be 50 mV rms and pin 1 should be connected
to the supply via a 100W resistor.
IF Amplifier DetectorThe IF amplifier is a wide band amplifier with a tuned output stage.
The IF filters can be either LC or mixed LC/ceramic.
AM detection occurs at pin 7. A detection capacitor is connected to pin 6 to reduce the radiation of spurious
detector products.
The Audio output is at pin 9 (for either AM or FM); the IF frequency is filtered by an external capacitor which
is also used as the FM mono de-enphasis network. The audio output impedance is about 7KΩ and a high
impedance load (~ 50KΩ) must be used.
AGCAutomatic gain control operates in two ways.
With weak signals it acts on the IF gain, maintaining the maximum S/N. For strong signals a second circuit
intervenes which controls the entire chain and allows signal handling in excess of one volt (m = 0.8).
At pin 8 there is a carrier envelope signal which is filtered by an external capacitor to remove the Audio and
RF content and obtain a mean DC signal to drive the AGC circuit.
TDA1220B
APPLICATION INFORMATION (continued)
FM Section
IF Amplifier and limiterThe 10.7 MHz IF signal from the ceramic filter is amplified and limited by a chain of four differential stages.
Pin 16 is the amplifier input and has a typical input impedance of 6.5 KW in parallel with 14 pF at 10.7 MHz.
Bias for the first stage is available at pin 14 and provides 100% DC feedback for stable operating conditions.
Pin 15 is the second input to the amplifier and is decoupled to pin 14, which is grounded by a 20 nF capacitor.
An RLC network is connected to the amplifier output and gives a 90° phase shift (at the IF centre frequency)
between pins 13 and 12. The signal level at pin 13 is about 150 mV rms
FM DetectorThe circuit uses a quadrature detector and the choise of component values is determined by the acceptable
level of distortion at a given recovered audio level.
With a double tuned network the linearity improves (distortion is reduced) and the phase shift can be
optimized; however this leads to a reduction in the level of the recovered audio. A satisfactory compromise
for most FM receiver applications is shown in the test circuit.
Care shoul be taken with the physical layout.
The main recommandations are:
• Locate the phase shift coil as near as possible to pin 13.
• Shunt pins 14 and 16 with a low value resistor (between 56Ω and 330Ω).
• Ground the decoupling capacitor of pin 14 and the 10.7 MHz input filter at the same point.
AM-FM SwitchingAM-FM switching is achieved by applying a DC voltage at pin 13, to switch the internal reference.
Typical DC voltages (refer to the test circuit)
TDA1220B
APPLICATION SUGGESTIONReccomended values are referred to the test circuit of Fig. 2.
(*) Only for test circuit
TDA1220B
APPLICATION INFORMATION (continued)
Figure 12. Portable AM/FM radio
TDA1220B
