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CXA1744AR

IF Amplifier for Digital Cordless Telephone

Sony Semiconductor 

CXA1744AR

3) Multiplier

The ×5 multiplier is provided in this IC for mixer local signal. The fifth-order component of the input signal is

extracted by the resonance circuit connected to Pin 44 externally. Wire the resonance circuit as close to

Pin 44 as possible.

4) Mixer

The CXA1744AR mixer is of double balanced type. Its input is at Pins 38 and 39; when input from Pin 39,

Pin 38 should be grounded with a capacitor.

5) 10.7 MHz filter

The mixer output impedance and IF amplifier input impedance are approximately 330 Ω. The IF amplifier

output impedance and limiter amplifier input impedance are approximately 460 Ω. Use the 10.7 MHz filter

with matching.

6) Detector

For quadrature FM detection, the phase of the limiter output (Pin 24) is shifted 90° by the RLC parallel

resonance circuit or discriminator as the output is input to pin 23.

The phase shifter by RLC parallel resonance circuit is shown below. In this case, values of L and C are

determined so that the center frequency of the second IF signal and the parallel resonance frequency are

equal. As the value of R sets the detector output level, select this value so as to obtain the required output

level.

With regards to the detector input, the center frequency of the second IF signal and the frequency for the

minimum value of the detector distortion does not match because the internal delay is more than the

external one. Add the delay circuit as shown below to match the center frequency of the second IF signal

and the frequency for the minimum value of the detector distortion.

Delay circuit

QDIN LIMOUT

23 24

L

C

R

RSSIVCC

—16—

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