AMIS-49200 Fieldbus MAU
Data Sheet
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, fL, of the high-pass filter is determined by C1 and C2 while cut-off frequency, fH,
of the low-pass filter is determined by C3 and C4.
RF2
RF1
1
1
1
2
fL =
QL =
=0.95
2π RF1*RF2*C1*C2
C3
1
1
fH
=
QL = 0.44*
=0.95
C4
2π RF3*RF4*C3*C4
The possible ranges of fL and fH are 1kHz ~ 10kHz and 10kHz ~ 100kHz, respectively. The values in the following figure are
recommended to obtain 1kHz and 47.6kHz cut-off frequencies.
Bandpass Filter
C3=220pf
FLTOUT
31
30 FLT
HPF
RF1
75K
To
Detectors
28
VCC
VCC
A2
RF4
54K
RF3
20K
C1
SIGIN
C2
A1
Signal
Input
27
1000pf
1000pf
RF2
270K
Vmid
29
C4=47pf
Figure 10: Band Pass Filter
4.4.2. Receive Signal Detection
The carrier detector generates the receive activity (RxA) signal by detecting the input signal amplitude. Minimum amplitude is 100mVp-
p (TYP). A delay, determined by the capacitor connected between the CCD pin and GND, is added to avoid detection of transient
noise. The recommended value of CCD is 100pF. The output can drive a CMOS input of VDD supply voltage.
The zero-cross detector generates the receive signal (RxS) with minimum phase error (jitter) by detecting the transition between high
and low levels of the incoming Manchester code. Hysteresis of +40mV (TYP) is applied to avoid unnecessary switching by noise.
Once the carrier-detect goes active the hysteresis is removed and the switching point threshold is set to Vmid. The output can drive a
CMOS input of VDD supply voltage.
AMI Semiconductor – Jan. 07, M-20532-003
17
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