AS8413 데이터 시트보기 (PDF) - austriamicrosystems AG
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AS8413 Datasheet PDF : 15 Pages
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High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
Analog Conditioning
The analog front-end, composed of a preamplifier and a filter centered at 40 kHz, increases the
signal level and removes noise outside the bandpass. It is followed by a digitally-controlled AGC
amplifier, that keeps signal level at the VCAP output within prescribed levels. Finally, an envelope
detector extracts the information embedded in the amplified echo signal.
The front-end needs proper bias during power-up. That can be provided by an RC series circuit
to VDD, as shown at Fig. 2, or alternatively, by the pre-amplifier of Fig. 4.
VDD
100n
100k To RX-Pin
Fig. 2 - Series-RC circuit at RX
The AS8413 has a wide dynamic range, to follow the signal fluctuations that occur in a large
variety of vehicles, sensors and environmental conditions. Only under extreme conditions, like in
a larger vehicle, an external pre-amplifier at RX may help to improve performance.
A practical way to verify if a pre-amplifier might be useful, is by monitoring the echo waveform at
VCAP. For measuring that voltage a FET-input buffer (input impedance at least 109 ohm) should
be used, as the output impedance at VCAP is very high.
A pre-amplifier that satisfies the bias requirements is shown at the Fig. 4. Its gain is around 8 dB.
VCAP(V)
3,0V-4,2V
1,3V-1,8V
0
10
20
30
Period = 44,4 ms
Fig. 3 - Waveform at VCAP
40
T(ms)
March 2001
Page 8 of 15
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