tda1599t-v3 NXP Semiconductors, tda1599t-v3 Datasheet - Page 5

• Manufacturer Part Number: tda1599t-v3
• Description: If Amplifier/demodulator For Fm Radio Receivers
• Manufacturer: NXP Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
The limiter amplifier has five stages of IF amplification
using balanced differential limiter amplifiers with emitter
follower coupling.
Decoupling of the stages from the supply voltage line and
an internal high-ohmic DC feedback loop give a very stable
IF performance. The amplifier gain is virtually independent
of changes in temperature.
The FM demodulator is fully balanced and compromises
two cross-coupled differential amplifiers. The quadrature
detection of the FM signal is performed by direct feeding of
one differential amplifier from the limiter amplifier output,
and the other via an external 90 degrees phase shifting
network. The demodulator has a good stability and a small
zero-cross-over shift. The bandwidth on the demodulator
output is restricted by an internal low-pass filter to
approximately 1 MHz.
Non-linearities, which are introduced by demodulation, are
compensated by the THD compensation circuit. For this
reason, the demodulator resonance circuit (between pins
10 and 11) must have a loaded Q-factor of 19.
May 1994
IF amplifier/demodulator for FM radio
receivers
5
Consequently, there is no need for the demodulator tuned
circuit to be adjusted for minimum distortion. Adjustment
criterion is a symmetrical stop pulse. The control voltage
for the mute attenuator (pin 16) is derived from the values
of the level detector and the detuning detector output
signals. The mute attenuator has a fast attack and a slow
decay determined by the capacitor on pin 16. The AF
signal is fed via the mute attenuator to the output (pin 4). A
weighted control voltage (pin 6) is obtained from the mute
attenuator control voltage via a buffer amplifier that
introduces an additional voltage shift and gain.
The level detector generates a voltage output signal
proportional to the amplitude of the input signal. The
unweighted level detector output signal is available in
FM-MUTE-ON condition (mode switch).
The open-collector tuning stop output voltages STOP-0
and STOP-1 (pins 15 and 14) are derived from the
detuning and the input signal level. The pins 14 and 15
may be tied together, if only one tuning-stop output is
required.
Product specification
TDA1599