TDA1220BK View Datasheet(PDF) - STMicroelectronics

Part Name

Description

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TDA1220BK

AM-FM QUALITY RADIO

STMicroelectronics 

TDA1220B

APPLICATION INFORMATION (continued)

FM Section

IF Amplifier and limiter

The 10.7 MHz IF signal from the ceramic filter is amplified and limited by a chain of four differential stages.

Pin 16 is the amplifier input and has a typical input impedance of 6.5 KW in parallel with 14 pF at 10.7 MHz.

Bias for the first stage is available at pin 14 and provides 100% DC feedback for stable operating conditions.

Pin 15 is the second input to the amplifier and is decoupled to pin 14, which is grounded by a 20 nF capacitor.

An RLC network is connected to the amplifier output and gives a 90° phase shift (at the IF centre frequency)

between pins 13 and 12. The signal level at pin 13 is about 150 mV rms

FM Detector

The circuit uses a quadrature detector and the choise of component values is determined by the acceptable

level of distortion at a given recovered audio level.

With a double tuned network the linearity improves (distortion is reduced) and the phase shift can be

optimized; however this leads to a reduction in the level of the recovered audio. A satisfactory compromise

for most FM receiver applications is shown in the test circuit.

Care shoul be taken with the physical layout.

The main recommandations are:

• Locate the phase shift coil as near as possible to pin 13.

• Shunt pins 14 and 16 with a low value resistor (between 56Ω and 330Ω).

• Ground the decoupling capacitor of pin 14 and the 10.7 MHz input filter at the same point.

AM-FM Switching

AM-FM switching is achieved by applying a DC voltage at pin 13, to switch the internal reference.

Typical DC voltages (refer to the test circuit)

Pins 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Unit

AM 9 1.4 9 1.4 1.4 8.4 9 0.7 1.9 9 0 0.1 0.1 8.5 8.5 8.5 V

FM 9 0.02 9 0.02 0.02 8.5 9 0 1.7 9 0 9 9 8 8 8 V

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