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TDA7421N

1.0 FM SECTION

Featuring a single conversion configuration, it comprises a multi-stage IF limiter whose gain is I

and a quadrature demodulator with detuning and adjacent channel detectors. Signal meter and stop station

functions are also supported

2.0 AM SECTION

AM signal is converted by means of UP-DOWN configuration (IF1 = 10.7MHz, IF2 = 450KHz) and MW/LW

bands are covered.

3.0 PLL SECTION

Three operating modes are available:

They are user programmable with the mode PM registers.

3.1 Standby mode

It stops all functions. This allows low current consumption without loss of information in all registers. The pin LP-

OUT is forced to 0V in power on. All data registers are set to FE (11111110). The oscillator does not run in stand-

by mode.

3.2 FM and AM Operation

The FM or AM signal applies to a 32/33 prescaler, which is controlled by a 5 bit counter (A). The 5 bit register

(PC0 to PC4) controls this divider.

The output of the prescaler connects to a 11 bit divider (B). The 11 bit register (PC5 to PC15) controls the divider 'B'.

3.2.1 THREE STATE PHASE COMPARATOR

The phase comparator generates a phase error signal according to phase difference between fSYN and fREF.

This phase error signal drives the charge pump current generator.

3.2.2 CHARGE PUMP CURRENT GENERATOR

This stage generates signed pulses of current. The phase error signal decides the duration and polarity of those

pulses.The current absolute values are programmable by A0, A1, A2 registers for high current and B0, B1 reg-

isters for low current.

3.2.3 LOW NOISE CMOS OP-AMP

An internal voltage divider at pin VREF connects the positive input of the low noise Op-Amp.The charge pump

output connects the negative input. This internal amplifier in cooperation with external components can provide

an active filter. The negative input is switchable to three input pins (LPIN 1, LPIN 2 and LPIN 3), to increase the

flexibility in application.This feature allows two separate active filters for different applications.A logical "1" in the

LPIN 1/2 register activates pin LPIN 1, otherwise pin LPIN 2 is active. While the high current mode is activated

LPIN 3 is switched on.

PM0

PM1

Operating Mode

0

0

Standby

10

AM

0

1

not used

11

FM