atr2732n1 ATMEL Corporation, atr2732n1 Datasheet - Page 6

• Manufacturer Part Number: atr2732n1
• Description: Integrated Dab One-chip Front End
• Manufacturer: ATMEL Corporation

3.2
6
AGC in General
ATR2732N1
Figure 3-1.
There are three AGCs in the ATR2732N1, 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:
Table 3-1.
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.
MSB
0
0
0
0
1
1
1
1
3)
1)
2)
Functional Block Diagram with Labelled Inputs and Outputs
Selection of Time Constant Factor
VCO
VCO
0
0
1
1
0
0
1
1
frac. PLL
L-band
PLL
VHF
4)
LSB
0
1
0
1
0
1
0
1
Vtune
Gain
gen.
cntl
Time Constant Factor
Infinite
32
16
8
4
2
1
0.2
5)
A
D
SPI interface
Control unit
RSSI
6)
PWR
cntl
9130AS–DAB–04/08
7)