ATA5282 Datasheet, PDF (5/23 Pages) ATMEL Corporation – ULTRA LOW POWER 125 KHZ 3D WAKE UP RECEIVER WITH RSSI

ATA5282 [Preliminary]
AGC Amplifier
Each of the three input stages contain an AGC amplifier to amplify the input signal from
the Coil. The gain is adjusted by the automatic gain control circuit if a preamble signal is
detected. The high dynamic range of the AGC amplifier enables the IC to work with input
signals from 2.8 mV_PP to 3.1 V_PP. After the AGC settling time has elapsed, the amplifier
output delivers a 125-kHz signal with an amplitude adjusted for the following evaluation
circuits (preamble detection, signal conditioner, wake-up).
Automatic Gain Control
For correct demodulation, the signal conditioner needs an appropriate internal signal
amplitude. To control the input signal, the ATA5282 has a built-in digital AGC for each
input channel. This gain control circuit regulates the internal signal amplitude to the ref-
erence level (Ref2, Figure 4 on page 6). The gain control uses the signal of the input
channel with the highest amplitude for the regulation as well as signal for the signal
conditioner.
During the preamble, each period of the carrier signal decreases the gain if the internal
signal exceeds the reference level. If the signal does not achieve the reference level,
each period increases the gain. After 192 preamble periods, the standard gain control
mode is activated. In this mode, the gain is decreased every two periods if the internal
signal exceeds the reference level and increased every eight periods if the reference
level is not achieved. These measures assure that the input signal’s envelope deforma-
tion will be minimized.
During the gaps between signal bursts, the gain control is frozen to avoid that the gain
be modified by noise signals.
The tuning range of the AGC is subdivided into 256 regulator steps. The settling time for
the full tuning range requires 320 periods (192 + (2 × 64) periods) during a preamble
phase. To accelerate the settling time, fast gain control mode can be activated via the
serial interface. In this mode, the tuning range is subdivided into 128 steps and the set-
tling time is two times faster.
In standby listen mode, the gain is reset to the maximum value. A proper carrier signal
activates the automatic gain control.
The preamble (Figure 9 on page 10) with up to 320 periods of the 125 kHz magnetic
field is used to control the gain of the input amplifiers. To detect the starting point of the
header, the start gap should not exceed 256 µs (32 periods of 125 kHz).
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