AMIS-49587_15 Datasheet, PDF (26/56 Pages) ON Semiconductor – Power Line Carrier Modem

AMIS−49587
6.3.2 50/60 Hz Suppression Filter
AMIS−49587 receiver input provides a low noise input
operational amplifier in a follower configuration which can
be used to make a 50/60 Hz suppression filter with a
minimum number of external components. Pin RX_IN is the
positive input and RX_OUT is the output of the input low
noise operational amplifier. The pin REF_OUT can be use
as an analog ground (1.65 V) for the external circuitry.
Received
C₂
Signal
R2
RX_OUT ₂
C₁
RX_IN 3
LOW NOISE
OPAMP
Receiver (S−FSK Demodulator)
TO AGC
R₁
REF_OUT 4
CDREF
REF
1,65 V
V SSA
Figure 21. External Component Connection for 50/60 Hz Suppression Filter
RX_IN is the positive analog input pin of the receiver low
noise input op−amp. Together with the output RX_OUT an
active high pass filter is realized. This filter removes the
main frequency (50 Hz or 60 Hz) from the received signal.
The filter characteristics are determined by external
capacitors and resistors. Typical values are given in
Table 26. For these values and after this filter, a typical
attenuation of 85 dB at 50 Hz is obtained. Figure 21
represents external components connection. In a typical
application the coupling transformer in combination with a
parallel capacitance forms a high pass filter with a typical
attenuation of 60 dB. The combined effect of the two filters
decreases the voltage level of 230 Vrms at the mains
frequency well below the sensitivity of the AMIS−49587.
20
−20
−60
−100
−140
10
100
1k
10k
Frequency (Hz)
Figure 22. Transfer Function of 50 Hz Suppression Circuit
REF_OUT is the analog output pin which provides the
voltage reference used by the A/D converter. This pin must
be decoupled from the analog ground by a 1 mF ceramic
capacitance (C_DREF). It is not allowed to load this pin.
The low noise operational amplifier can be bypassed and
powered down by setting the bit R_RX_MOD[7] to 1. In this
mode the pin RX_OUT must be used as input of the AGC.
100k
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