AMIS-49200 Datasheet, PDF (13/19 Pages) AMI SEMICONDUCTOR – Fieldbus MAU Chip

AMIS−49200
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.
Ǹ f_L
+
1
2p
R_F1
1
R_F2 C₁
C₂
Ǹ Q_L
+
1
2
R_F2
R_F1
+
0.95
(eq. 5)
Ǹ f_H
+
1
2p
R_F3
1
R_F4 C₃
C₄
Ǹ Q_L + 0.44
C₃
C₄
+
0.95
(eq. 6)
The possible ranges of f_L and f_H are 1 kHz ~ 10 kHz and
10 kHz ~ 100 kHz, respectively. The values in the following
figure are recommended to obtain 1 kHz and 47.6 kHz
cut-off frequencies.
FLTOUT 31
C3 = 220 pF _{30 FLT}
To Detectors
VCC
−
A2
+
RF4
RF3
54 kW 20 kW
29
C4 = 47 pF
RF1
75 kW
VCC
−
A1
+
RF2
270 kW
HPF
28
SIGIN
27
C2
1000 pF
C1
1000 pF
Signal Input
Vmid
Figure 10. Band Pass Filter
Receive Signal Detection
The carrier detector generates the receive activity (RxA)
signal by detecting the input signal amplitude. Minimum
amplitude is 100 mVp-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 100 pF. 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 +40 mV (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.
Zero-cross Detector
RXS
35
VDD
Level
Convert
RXA
34
CCD
32
VDD
Level
Convert
VCC
+
C1
−
ZC Tript Pt
Vtrip = Vmid
Vhyst = +40 mV
Carrier Detector _VCC
VCC
+
C2
−
VHi50
CD_Output
VCC
+
C2
−
VLo50
RxSig
Vmid
R
(1 MW)
C
(60 pF)
VHi50 = Vmid + 50 mV
Vlo50 = Vmid − 50 mV
Filtered received
signal from
Bandpass Filter
Figure 11. Receive Signal Detectors
http://onsemi.com
13