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SA608DK
Low voltage high performance mixer FM IF system
Philips Semiconductors RF Communications Products Product specification
SA608Low voltage high performance mixer FM IF system
DESCRIPTIONThe SA608 is a low voltage high performance
monolithic FM IF system incorporating a
mixer/oscillator, two limiting intermediate
frequency amplifiers, quadrature detector,
logarithmic received signal strength indicator
(RSSI), voltage regulator and audio and RSSI
op amps. The SA608 is available in 20-lead
dual-in-line plastic, 20-lead SOL
(surface-mounted miniature package) and
20-lead SSOP package.
The SA608 was designed for portable
communication applications and will function
down to 2.7V. The RF section is similar to
the famous NE605. The audio output is
buffered. The RSSI output has an internal
amplifier with the feedback pin accessible.
The SA608 also has an extra limiter output.
This signal is buffered from the output of the
limiter and can be used to perform frequency
check. This is accomplished by comparing a
reference frequency with the frequency check
signal using a comparator to a varactor or
PLL at the oscillator inputs.
FEATURES Low power consumption: 3.5mA typical at Mixer input to >150MHz Mixer conversion power gain of 17dB at
45MHz XTAL oscillator effective to 150MHz (L.C.
oscillator or external oscillator can be used
at higher frequencies) 102dB of IF Amp/Limiter gain 2MHz limiter small signal bandwidth Temperature compensated logarithmic
Received Signal Strength Indicator (RSSI)
with a 90dB dynamic range Low external component count; suitable for
crystal/ceramic/LC filters Excellent sensitivity: 0.31μV into 50Ω
matching network for 12dB SINAD (Signal
to Noise and Distortion ratio) for 1kHz tone,
8kHz deviation with RF at 45MHz and IF at
455kHz SA608 meets cellular radio specifications Audio output internal op amp RSSI output internal op amp Buffered frequency check output Internal op amps with rail-to-rail outputs ESD protection: Human Body Model 2kV
Robot Model 200V
APPLICATIONS Portable cellular radio FM IF Cordless phones Narrow band cellular applications
(NAMPS/NTACS) RF level meter Spectrum analyzer Instrumentation FSK and ASK data receivers Log amps Portable high performance communication
receivers Single conversion VHF receivers Wireless systems
PIN CONFIGURATION
ORDERING INFORMATION
Philips Semiconductors RF Communications Products Product specification
SA608Low voltage high performance mixer FM IF system
BLOCK DIAGRAM
ABSOLUTE MAXIMUM RATINGS
DC ELECTRICAL CHARACTERISTICSVCC = +3V, TA = 25°C; unless otherwise stated.
Philips Semiconductors RF Communications Products Product specification
SA608Low voltage high performance mixer FM IF system
AC ELECTRICAL CHARACTERISTICSTA = 25°C; VCC = +3V, unless otherwise stated. RF frequency = 45MHz + 14.5dBV RF input step-up; IF frequency = 455kHz; R17 = 2.4k; R18
= 3.3k; RF level = –45dBm; FM modulation = 1kHz with ±8kHz peak deviation. Audio output with de-emphasis filter and C-message weighted
filter. Test circuit 1. The parameters listed below are tested using automatic test equipment to assure consistent electrical characterristics. The
limits do not represent the ultimate performance limits of the device. Use of an optimized RF layout will improve many of the listed parameters.
NOTE: The generator source impedance is 50Ω, but the SA608 input impedance at Pin 18 is 1500Ω. As a result, IF level refers to the actual signal
that enters the SA608 input (Pin 18) which is about 21dB less than the “available power” at the generator. By using 45kΩ load across the Quad detector coil, you will have Audio output at 115mV with –42dB distortion.
Philips Semiconductors RF Communications Products Product specification
SA608Low voltage high performance mixer FM IF system
CIRCUIT DESCRIPTIONThe SA608 is an IF signal processing system
suitable for second IF systems with input fre-
quency as high as 150MHz. The bandwidth
of the IF amplifier and limiter is at least 2MHz
with 90dB of gain. The gain/bandwidth dis-
tribution is optimized for 455kHz, 1.5kΩ
source applications. The overall system is
well-suited to battery operation as well as
high performance and high quality products
of all types.
The input stage is a Gilbert cell mixer with
oscillator. Typical mixer characteristics
include a noise figure of 6.2dB, conversion
gain of 17dB, and input third-order intercept
of –9dBm. The oscillator will operate in
excess of 200MHz in L/C tank configurations.
Hartley or Colpitts circuits can be used up to
100MHz for xtal configurations. Butler
oscillators are recommended for xtal
configurations up to 150MHz.
The output impedance of the mixer is a 1.5kΩ
resistor permitting direct connection to a
455kHz ceramic filter. The input resistance
of the limiting IF amplifiers is also 1.5kΩ.
With most 455kHz ceramic filters and many
crystal filters, no impedance matching
network is necessary. The IF amplifier has
43dB of gain and 5.5MHz bandwidth. The IF
limiter has 60dB of gain and 4.5MHz
bandwidth. To achieve optimum linearity of
the log signal strength indicator, there must
be a 12dB(v) insertion loss between the first
and second IF stages. If the IF filter or
interstage network does not cause 12dB(v)
insertion loss, a fixed or variable resistor or
an L pad for simultaneous loss and
impedance matching can be added between
the first IF output (Pin 16) and the interstage
network. The overall gain will then be 90dB
with 2MHz bandwidth.
The signal from the second limiting amplifier
goes to a Gilbert cell quadrature detector.
One port of the Gilbert cell is internally driven
by the IF. The other output of the IF is
AC-coupled to a tuned quadrature network.
This signal, which now has a 90° phase
relationship to the internal signal, drives the
other port of the multiplier cell.
The demodulated output of the quadrature
drives an internal op amp. This op amp is
configured as a unity gain buffer.
A log signal strength completes the circuitry.
The output range is greater than 90dB and is
temperature compensated. This log signal
strength indicator exceeds the criteria for
AMPs or TACs cellular telephone. This
signal is buffered through an internal unity
gain op amp. The frequency check pin
provides a buffered limiter output. This is
useful for implementing an AFC (Automatic
Frequency Check) function. This same
output can also be used in conjunction with
limiter output (Pin 11) for demodulating FSK
(Frequency Shift Keying) data. Both pins are
of the same amplitude, but 180° out of phase.
NOTE: Limiter or Frequency Check output
has drive capability of a 5kΩ minimum or
higher in order to obtain 120mVRMS output
level.
NOTE: dB(v) = 20log VOUT/VIN
Philips Semiconductors RF Communications Products Product specification
SA608Low voltage high performance mixer FM IF system
Philips Semiconductors RF Communications Products Product specification
SA608Low voltage high performance mixer FM IF system
Philips Semiconductors RF Communications Products Product specification
SA608Low voltage high performance mixer FM IF system
NOTES: C-message: The C-message and de-emphasis filter combination has a peak gain of 10 for accurate measurements. Without the gain, the
measurements may be affected by the noise of the scope and HP339 analyzer. The de-emphasis filter has a fixed -6dB/Octave slope be-
tween 300Hz and 3kHz. Ceramic filters: The ceramic filters can be 30kHz SFG455A3s made by Murata which have 30kHz IF bandwidth (they come in blue), or
16kHz CFU455Ds, also made by Murata (they come in black). All of our specifications and testing are done with the more wideband filter. RF generator: Set your RF generator at 45.000MHz, use a 1kHz modulation frequency and a 6kHz deviation if you use 16kHz filters, or
8kHz if you use 30kHz filters. Sensitivity: The measured typical sensitivity for 12dB SINAD should be 0.35μV or –116dBm at the RF input. Layout: The layout is very critical in the performance of the receiver. We highly recommend our demo board layout. RSSI: The smallest RSSI voltage (i.e., when no RF input is present and the input is terminated) is a measure of the quality of the layout and
design. If the lowest RSSI voltage is 500mV or higher, it means the receiver is in regenerative mode. In that case, the receiver sensitivity
will be worse than expected. Supply bypass and shielding: All of the inductors, the quad tank, and their shield must be grounded. A 10-15μF or higher value tantalum
capacitor on the supply line is essential. A low frequency ESR screening test on this capacitor will ensure consistent good sensitivity in pro-
duction. A 0.1μF bypass capacitor on the supply pin, and grounded near the 44.545MHz oscillator improves sensitivity by 2-3dB. R5 can be used to bias the oscillator transistor at a higher current for operation above 45MHz. Recommended value is 22kΩ, but should not
be below 10kΩ.
