AMIS-492X0 Datasheet, PDF (16/22 Pages) ON Semiconductor – Fieldbus MAU

AMIS-492x0
Figure 10: Current Control Circuit
4.4 Receive Block
The receive block contains three sub-blocks, which are internally connected:
1. A band pass filter – to filter the desired incoming communication signal.
2. Carrier detector – generates the RxA signal by detecting the signal amplitude.
3. Zero-cross detector generates the RxS signal by detecting the high/low transitions of the Manchester code.
4.4.1. Band Pass Filter
The band pass filter is a series connection of a high-pass and a low-pass filters each having two poles. Each filter is comprised of a
voltage follower and on chip resisters, so only four external capacitors are necessary. The following figure shows an internal circuit and
the connection of external capacitors. Cut-off frequency, f_L, of the high-pass filter is determined by C₁ and C₂ while cut-off frequency, f_H,
of the low-pass filter is determined by C₃ and C₄.
f_L
=
1
2π
1
R _F1*R _F2 *C₁*C₂
f_H
=
1
2π
1
R _F3*R _F4 *C₃*C₄
Q_L
=
1
2
R _F2
R _F1
=0.95
Q_L = 0.44 *
C₃
C₄
=0.95
The possible ranges of f_L and f_H are 1kHz ~ 10kHz and 10kHz ~ 100kHz, respectively. The values in the following figure are
recommended to obtain 1kHz and 47.6kHz cut-off frequencies.
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