Quadrature Demodulator - ON Semiconductor NCN49597 Manual

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Table Of Contents

Table of Contents

RX_OUT

REF_OUT

FROM

ANALOG

Noise

Shaper

GAIN

Figure 19. Digital Path of the Receiver ADC and Quadrature Demodulation

50/60 Hz Suppression Filter

NCN49597 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

Received

Signal

Figure 20. 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 or 60 Hz) from the received signal. The

filter characteristics are determined by external capacitors

and resistors. Typical values are given in Table 27. For these

LOW NOISE

OPAMP

RX_IN

1,65 V

Figure 18. Analog Path of the Receiver

Receiver (Digital Path)

Compen−

Decimator

sator

Abs

AGC

value

Control

accu

RX_OUT

RX_IN

REF_OUT

DREF

SSA

http://onsemi.com

NCN49597

Receiver (Analog Path )

4th

LPF

order

Gain

SD AD

REF

PC20090610.2

FROM TRANSMITTER

Decimator

noise operational amplifier. REF_OUT is the analog output

pin which provides the voltage reference (1.65 V) used by

the A/D converter. This pin must be decoupled from the

analog ground by a 1 mF ceramic capacitance (C

not allowed to load this pin.

Receiver (S− FSK Demodulator)

LOW NOISE

OPAMP

TO AGC

REF

1,65 V

values and after this filter, a typical attenuation of 85 dB at

50 Hz

obtained. Figure 21

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

FROM

DIGITAL