Atmel ATA5283 - Manual (Page 4)

4
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 k
Ω
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. 1 Gap detection
reference
Ref. 2
100%
50%
Gain control
reference
Transmitted
signal