Atmel ATA5283 - Manual (Page 3)

3
4598H–AUTO–03/07
ATA5283
3. Functional Description
The ATA5283 is an ultra-low power ASK receiver. Without a carrier signal it operates in the
standby listen mode. In this mode it monitors the coil input with a very low current consumption.
To activate the IC and the connected control unit, the transmitting stage must send the preamble
carrier burst. After a preamble is detected the IC is activated. It adapts the gain of the input stage
and enables the wake-up and the data output. The first gap at the end of the preamble gener-
ates a wake-up signal for the microcontroller. After that the receiver outputs the data signal at
N_DATA. To return the IC into the standby listen mode it must be reset via the RESET input.
3.1 AGC Amplifier
The input stage contains an Automatic Gain Control (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 enables the IC to operate with input signals from
1 mV
rms
to 1.1V
rms
. After the AGC settling time the amplifier output delivers a 125 kHz signal with
an amplitude adjusted for the following evaluation circuits’ preamble detection, signal condi-
tioner, wake-up.
3.2 Preamble Detection
Before data transmission the IC stays in standby listen mode. To prevent the circuit from unin-
tended operations in a noisy environment the preamble detection circuit checks the input signal.
A valid signal is detected by a counter after 192 carrier periods without interrupts. Short inter-
rupts which are suppressed by the signal conditioner are tolerated. When a valid carrier
(preamble) is found the circuit starts the automatic gain control. It requires up to 512 carrier peri-
ods to settling. The complete preamble should have 704 carrier periods minimum. The preamble
is terminated and the data transfer is started with the first gap (Start Gap) in the carrier (see
Fig-
ure 3-1 ).
Figure 3-1. Communication Protocol
Data
Start
gap
0.5 µA 2 µA
1 µA
Preamble
> 5.64 ms
Procedure
Current
profile
Gain
control
RESET
N_WAKEUP
N_DATA
Signal
192 Periods
of LF
> 512 Periods
of LF
AGC
adjustment
No gain
control
No gain
control
Gain control
active