AMIS-49200 Datasheet, PDF (17/22 Pages) AMI SEMICONDUCTOR – Fieldbus MAU Chip

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, 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.
To
Detectors
C3=220pf
31 FLTOUT
30 FLT
VCC
A2
RF4
RF3
54K
20K
29
C4=47pf
Bandpass Filter
RF1
75K
VCC
A1
HPF
28
RF2
270K
SIGIN C2
27
1000pf
Vmid
C1
1000pf
Signal
Input
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 C_CD is 100pF. The output can drive a CMOS input of V_DD 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 V_DD supply voltage.
AMI Semiconductor – Jan. 07, M-20532-003
17
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