4

ATA5283 [Preliminary]

4598D–AUTO–03/04

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 regulates the internal signal amplitude to the reference value (Ref2, Fig-

ure 4). 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 k

Ω because of the internal regulator circuit (see Figure 10).

Figure 4. Automatic Gain Control

Transmitted

signal

Gain controlled

signal

Gain control

reference

Gap detection

reference

Ref.1

Ref.2

Coil

input

N_DATA

Internal comparator

singal