U4311B Datasheet, PDF(5/14 Page) TEMIC Semiconductors – Low-current Superhet Remote Control Receiver

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U4311B Datasheet, PDF (5/14 Pages) TEMIC Semiconductors – Low-current Superhet Remote Control Receiver

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TELEFUNKEN Semiconductors

U4311B

Circuit Description

General functions

The integrated circuit U4311B includes the following

functions: IF-amplifier, FM-demodulator, wake-up

circuit with monoflop, operational-amplifier, non-

inverting data comparator and voltage-regulator.

The 10.7 MHz IF-signal from the front end passes the

integrated IF-amplifier which operates for amplitude- or

frequency-modulated signals to either a logarithmic AM-

demodulator which was implemented to avoid settling

time problems effected by use of an automatic gain

control system or a quadrature detector for FM. A data

* shaping filter advantageously realized with the

* internal high performance operational-amplifier

reduces system bandwidth to an optimized compromise

regarding transmission distance and data recognition.

Thus, an optimal bit error rate can be achieved without

any further active component.

The comparator connected to the output of the filter has

a level-dependent hysteresis and clamps its reference

voltage to the signal minimum and maximum peaks as

described later.

* * Without IF-input signal in the normal mode only the

IF-amplifier and the AM demodulator which operates as

a level strength indicator are activated. If the level of the

IF signal increases, the whole circuitry is turned on by the

wake-up circuit. This signal is externally available at

pin 10 and can be used to wake up a microcontroller.

After an adjustable reset time, determined by the mono-

flop time constant, the integrated circuit rests down to the

sleep mode. In this case typically 1 mA supply current is

required. An external resistor matched at pin 3 to ground

blocks the wake-up circuit and gives fully function at

lower IF-level as to recognize in figures 24 and 27, but

supply current increases up to typically 2.8 mA.

Function of the clamping comparator

The output signal of the operational amplifier is fed to the

input of the non-inverting comparator and two peak

detectors (Q1 and Q2, figure 3). Their time constants are

distinguished by RC+ and RCâ. The components value

must be adapted to the transmission code. The time

constant should be large compared to the bit-rate for opti-

mized noise and hum suppression. To compensate the

input transistors base-emitter-voltage differences these

two signals are buffered by Q3 and Q4. The mean value

is used as comparator threshold, the difference of the peak

values controls the hysteresis. This clamping comparator

works as a data regenerator.

Another version of the IC, with an inverting clamping

comparator, is also available (U4313B). Therefore the

operational amplifier can be used either as a non-

inverting or an inverting filter without the need of any

additional components.

VRef

95 9969

Op. amp.

+â

to pin 16

Comparator

Hysteresis

Comp. threshold

Rev. A1: 23.06.1995

Figure 3. Principle function of the clamping comparator

5 (14)

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