AMIS-492X0 Datasheet, PDF (17/22 Pages) ON Semiconductor – Fieldbus MAU

AMIS-492x0
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 11: 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.
Zero-Cross Detector
VDD
RXS
35
Level
Convert
VDD
RXA
34 Level
Convert
CCD
32
VCC
C1
ZC Tript Pt ^{Vtrip = Vmid}
Vhyst = + 40mV
Carrier Detector
VCC
VCC
C2
VHi50
CD_Output
VCC
C2
VLo50
RxSig
Vmid
R
(1Meg)
C
(60pF)
VHi50 = Vmid + 50mV
VLo50 = Vmid - 50mV
Filtered received signal
from Bandpass Filter
Figure 12: Receive Signal Detectors
Rev. 6 | Page 17 of 22 | www.onsemi.com