6

9129AS–DAB–04/08

ATR2732N3

Figure 3-1.

Functional Block Diagram with Labelled Inputs and Outputs

3.2

AGC in General

There are three AGCs in the ATR2732N3, one for the RF signals (around the LNAs) (1) and (3),

one for the very beginning of the IF path (mainly VHF mixer), and one for the IF amplifiers (5)

down to the output to baseband (7).

In these AGCs, the output signals of the relevant blocks are amplified, weakly band-pass fil-

tered, rectified, and, finally, low-pass filtered. The voltage derived in this power-measurement

process is compared to a voltage threshold which can be digitally controlled by several bits,

independently of each other. The setting is done via the control bus. Depending on the result of

this comparison, charge pumps feed a positive or negative current in order to charge or dis-

charge external capacitors. The voltage of these external capacitors is used to control the gains

of practically all blocks in the signal path.

By means of the control bus, the current of the AGC charge pump can be selected as specified

in the following table:

The input pin WAGC, set to logical 1, always sets all AGCs to time constant Infinite (meaning

there is practically no current to the AGC capacitors), regardless of the actual status of the bus

settings.

Control unit

SPI interface

RSSI

VCO

L-band

PLL

Gain

cntl

PWR

cntl

Vtune

gen.

VCO

VHF

frac. PLL

A

D

3)

1)

2)

4)

5)

6)

7)

Table 3-1.

Selection of Time Constant Factor

MSB

LSB

Time Constant Factor

00

0

Infinite

00

1

32

01

0

16

01

1

8

10

0

4

10

1

2

11

0

1

11

1

0.2