MC13027 Просмотр технического описания (PDF) - Motorola => Freescale

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MC13027

AMAX STEREO IC CHIPSET

Motorola => Freescale 

MC13027 MC13122

Figure 4. MC13027 Internal Block Diagram

WB AGC

Audio

Audio

Audio Blank

RF Blank

Out

Blank Time Blank Pulse Delay Time

IF Out

Time

IF In

20

19

18

17

16

15

14

Gnd2

13

RF Blank

12

Mixer Out

11

AF Time

MV

WB AGC Amp

AF Del

MV

IF Amp

RF Time

MV

NB Amp

VCC Mixer

X1

÷4

Reg

X1

1

2

3

4

5

6

7

8

WB AGC

Blanker

Feedback 4.0 V Reg

RF Gnd

Mixer In

4.0 Filter

VCC

In

AGC

Blanker RF In

9

10

VCO

LO Out

MC13027 FUNCTIONAL DESCRIPTION

The MC13027 contains the mixer, wide band AGC

system, local oscillator, IF pre–amplifier and noise blanker for

an AM radio receiver. It is designed to be used with the

MC13122 to produce a complete AM stereo receiver. The

VCO runs at 4 (Fin+FIF) and is divided internally by 4 for the

mixer input and local oscillator buffered output. Dividing the

VCO reduces the phase noise for AM stereo applications.

The noise blanker input is connected in parallel with the

mixer input at Pin 6. The noise blanker circuitry contains a

high gain amplifier with its own AGC so it remains linear

throughout the mixer’s linear range. It can detect noise

pulses as low as 120 µV and generates three pulses when

the noise threshold is exceeded. The width and timing of the

blanking pulses is set by the resistors connected to Pins 15,

17 and 19. The resistor on Pin 15 sets the length of the RF

blanking pulse and determines the time the transistor on

Pin 12 is “on”. The audio blanking pulse delay is set by the

resistor on Pin 17 and the width by the resistor on Pin 19.

This is necessary because the IF filtering delays and

stretches the noise as it arrives at the detector. The transistor

on Pin 18 goes “on” to cause noise blanking in the track and

hold circuit in the MC13122 (Pin 15).

Wideband AGC is used in auto receivers to prevent

overload – it drives the base of a cascode transistor RF

amplifier and also a pin diode at the antenna (See Figures 6

and 7).

A low gain IF amplifier between Pins 14 and 16 is used as

a buffer amplifier between the mixer output filter and IF filter.

The input resistance of the IF amplifier is designed to match

a ceramic IF filter. The gain of the IF amplifier is determined

by the impedance of the load on Pin 16.

MOTOROLA ANALOG IC DEVICE DATA

7

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