BLOCK DIAGRAM

Pin FUNCTION

No

Name

Function

1-2

XTAL OSCILLATOR

Connections for the Colpitts XTAL Oscillator.

The XTAL may be replaced by an inductor (see Figure 5) if the application

does not require high stability.

3

MIXER OUT

The Mixer is double balanced to reduce spurious products. The output

impedance is 1.8kW to match the input impedance of a 455kHz ceramic filter.

4

SUPPLY VOLTAGE

Must be well decoupled with a 100nF ceramic capacitor.

5

IF LIMITER INPUT

Input pin of the six stages amplifier with about 50

µV limiting sensitivity and

1.8k

Ω input impedance. The if output is connected to the external quadrature

coil (Pin 8) via an internal 10pF capacitor.

6-7

DECOUPLING

Good quality 100nF ceramic capacitors and a suitable layou are important.

8

QUADRATURE COIL

A quadrature detector is uded to demodulate the 455kHz FM signal. The Q of

the quad coil has direct effect on output level and distorsion (see Figure 6).

9

AUDIO OUTPUT SIGNAL

The audio output signal is buffered by an internal emitter follower.

10

OPERATIONAL

AMPLIFIER INPUT

Because of the low DC bias, the swing on the operational amplifier output is

11

OPERATIONAL

AMPLIFIER OUTPUT

This can be increased by adding a resistor from the operational amplifier input

to ground.

12

SQUELCH INPUT

The squelch trigger circuit with a low bias on the input (Pin 12) will force Pin

13 high ; and Pin 14 low.

13

SCAN CONTROL

Pulling Pin 12 above mute threshold (0.65V) will force Pin 13 to an impedance

of about 60k

Ω to ground and Pin 14 will be an open circuit.

14

MUTE

An hysteresis of about 50mV at Pin 12 will effectively prevent jitter.

15

GND

Ground Connection

16

10.7MHz MIXER INPUT

Input of the Wide-band Mixer. Normally used as 10MHz/455kHz converter, it

can be also used with input frequencies up to 60MHz.

TDA7361

2/8