Philips Semiconductors
Product specification
AM receiver circuit
GENERAL DESCRIPTION
TDA1572
The TDA1572 integrated AM receiver circuit performs all the active functions and part of the filtering required of an AM
radio receiver. It is intended for use in mains-fed home receivers and car radios. The circuit can be used for oscillator
frequencies up to 50 MHz and can handle RF signals up to 500 mV.
RF radiation and sensitivity to interference are minimized by an almost symmetrical design. The controlled-voltage
oscillator provides signals with extremely low distortion and high spectral purity over the whole frequency range, even
when tuning with variable capacitance diodes. If required, band switching diodes can easily be applied. Selectivity is
obtained using a block filter before the IF amplifier.
Features
•
Inputs protected against damage by static discharge
•
Gain-controlled RF stage
•
Double balanced mixer
•
Separately buffered, voltage-controlled and temperature-compensated oscillator, designed for simple coils
•
Gain-controlled IF stage with wide AGC range
•
Full-wave, balanced envelope detector
•
Internal generation of AGC voltage with possibility of second-order filtering
•
Buffered field strength indicator driver with short-circuit protection
•
AF preamplifier with possibilities for simple AF filtering
•
Electronic standby switch
•
IF output for stereo demodulator and search tuning.
QUICK REFERENCE DATA
PARAMETER
Supply voltage range
Supply current range
RF input voltage
for (S+N)/N = 6 dB at m = 30%
RF input voltage for 3% total
harmonic distortion (THD) at m = 80%
IF output voltage with V
i
= 2 mV
AF output voltage with V
i
= 2 mV;
f
i
= 1 MHz; m = 30%; f
m
= 400 Hz
AGC range: change of V
i
for
1 dB change of V
o(AF)
Field strength indicator voltage at V
i
= 500 mV;
R
L(11)
= 2,7 kΩ
PACKAGE OUTLINE
18-lead DIL; plastic (SOT102); SOT102-1; 1996 August 12.
V
IND
−
2,8
−
V
−
86
−
dB
V
o(AF)
−
310
−
mV
V
i(RF)
V
o(IF)
−
−
500
230
−
−
mV
mV
V
i(RF)
−
1,5
−
µV
V
P
I
P
SYMBOL
15
MIN.
7,5
−
−
TYP.
MAX.
18,0
30
V
mA
UNIT
December 1987
2
Philips Semiconductors
Product specification
AM receiver circuit
FUNCTIONAL DESCRIPTION
Gain-controlled RF stage and mixer
TDA1572
The differential amplifier in the RF stage employs an AGC negative feedback network to provide a wide dynamic range.
Very good cross-modulation behaviour is achieved by AGC delays at the various signal stages. Large signals are
handled with low distortion and the (S+N)/N ratio of small signals is improved. Low noise working is achieved in the
differential amplifier by using transistors with low base resistance.
A double balanced mixer provides the IF output signal to pin 1.
Oscillator
The differential amplifier oscillator is temperature compensated and is suitable for simple coil connection. The oscillator
is voltage-controlled and has little distortion or spurious radiation. It is specially suitable for electronic tuning using
variable capacitance diodes. Band switching diodes can easily be applied using the stabilized voltage V
13-18
. An extra
buffered oscillator output (pin 12) is available for driving a synthesizer. If this is not needed, resistor R
L(12)
can be omitted.
Gain-controlled IF amplifier
This amplifier comprises two cascaded, variable-gain differential amplifier stages coupled by a band-pass filter. Both
stages are gain-controlled by the AGC negative feedback network. The IF output is available at pin 10.
Detector
The full-wave, balanced envelope detector has very low distortion over a wide dynamic range. Residual IF carrier is
blocked from the signal path by an internal low-pass filter.
AF preamplifier
This stage preamplifies the audio frequency output signal. The amplifier output has an emitter follower with a series
resistor which, together with an external capacitor, yields the required low-pass for AF filtering.
AGC amplifier
The AGC amplifier provides a control voltage which is proportional to the carrier amplitude. Second-order filtering of the
AGC voltage achieves signals with very little distortion, even at low audio frequencies. This method of filtering also gives
fast AGC settling time which is advantageous for electronic search tuning. The AGC settling time can be further reduced
by using capacitors of smaller value in the external filter (C16 and C17). The AGC voltage is fed to the RF and IF stages
via suitable AGC delays. The capacitor at pin 7 can be omitted for low-cost applications.
Field strength indicator output
A buffered voltage source provides a high-level field strength output signal which has good linearity for logarithmic input
signals over the whole dynamic range. If the field strength information is not needed, R
L(11)
can be omitted.
Standby switch
This switch is primarily intended for AM/FM band switching. During standby mode the oscillator, mixer and AF
preamplifier are switched off.
Short-circuit protection
All pins have short-circuit protection to ground.
December 1987
4
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