Atmel ATA5283 3.3 Automatic Gain Control

4598H–AUTO–03/07

ATA5283

3.3 Automatic Gain Control

For a correct demodulation the signal conditioner needs appropriate internal signal amplitude.

To control the input signal the ATA5283 has a build in digital AGC. The gain control circuit regu-

lates the internal signal amplitude to the reference value (Ref2, Figure 3-2). It decreases the

gain by one step if the internal signal exceeds the reference level for two periods and it

increases the gain by one step if eight periods do not achieve the reference level. In the standby

listen mode the gain is reset to the maximum value. If a valid preamble signal (192 valid carrier

clocks) is detected the automatic gain control is activated.

Note: With the variation of the gain the coil input impedance changes from high impedance to minimal

143 kΩ because of the internal regulator circuit (see Figure 3-8 on page 8).

Figure 3-2. Automatic Gain Control

N_DATA

Internal comparator

signal

Gain controlled

signal

Coil

input

Ref. 1Gap detection

reference

Ref. 2

100%

50%

Gain control

reference

Transmitted

signal