1

Publication D/118/3 July 1994

CML Semiconductor Products

PRODUCT INFORMATION

Duplex Frequency Inverter

for Cordless Telephones

FX118

Features/Applications

Frequency Inversion Scrambling

Full-Duplex Operation

High Baseband and Carrier

Rejection

Audio Lowpass and Bandpass

Filtering On-Chip

Xtal Oscillator Stabilty

Low Power Requirement

(3.0 Volt Minimum)

Cordless Telephones

Base and Handheld Applications

Input Gain Adjustment

Plastic DIL and S.O.I.C. Package

Styles

FX118

C1 AMP OUT

C1 IN

LPF(1) OUT

B MOD(1) IN

C1 OUT

LPF(1)

INPUT AMP

BAL MOD (1)

BPF(1)

LPF(2) OUT

B MOD(2) IN

C2 AMP OUT

C2 IN

LPF(2)

BAL MOD (2)

BPF(2)

C2 OUT

CLOCKS

and

LOGIC

XTAL/CLOCK

CARRIER

3.3kHz

FILTER CLOCKS

111kHz

V

BIAS

INPUT AMP

V

BIAS

V

BIAS

XTAL

CHANNEL 1 (C1)

CHANNEL 2 (C2)

+0.5dB

-4.0dB

+4.0dB

+0.5dB

-4.0dB

+4.0dB

Fig.1 FX118 Duplex Frequency Inverter

Brief Description

The FX118 is a low-power, full-duplex frequency

inverter available to provide voice privacy for cordless

telephone systems by mixing the incoming audio with an

internally produced carrier frequency (3.3kHz).

This chip contains two completely separate audio

channels (C1 and C2) each comprising a “component-

adjustable” input amplifier, a 10th-order lowpass filter, a

balanced modulator and a 14th-order bandpass filter

output.

The on-chip modulation process has the properties of

high baseband and carrier frequency rejection which

when combined with high-order output filtering,

produces a high-quality recovered voiceband audio.

The frequency stability of the FX118 is achieved by an

on-chip oscillator employing an external 4.433619MHz

Xtal or clock input to produce the common carrier

frequency and the sampling clocks for the switched

capacitor low and bandpass filters.

This microcircuit has a low power requirement of 3.0

volts (min.) and is encapsulated in either 16-pin DIL or

small outline SMD (S.O.I.C.) plastic packages both of

which are of a physical size suitable for either base or

handset type telephone instruments as well as battery-

portable and mobile communications systems.