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CXA3185/3186N

Description of Functions

The CXA3185/3186N is a terrestrial wave broadcast tuner IC which converts frequencies to IF in order to

tune and detect only the desired reception frequency of VHF, CATV and UHF band signals.

In addition to the mixer, local oscillator and IF amplifier circuits required for frequency conversion to IF, this

IC also integrates a PLL circuit for local oscillator frequency control onto a single chip.

The functions of the various circuits are described below.

1. Mixer circuit

This circuit outputs the frequency difference between the signal input to VHFIN or UHFIN and the local

oscillation signal.

2. Local oscillator circuit

A VCO is formed by externally connecting an LC resonance circuit composed of a varicap diode and

inductance.

3. IF amplifier circuit

This circuit amplifies the mixer IF output, and consists of an amplifier stage and low impedance output

stage.

4. PLL circuit

This PLL circuit fixes the local oscillator frequency to the desired frequency. It consists of a prescaler, main

divider, reference divider, phase comparator, charge pump and reference oscillator. The control format

supports the 3-wire bus format. The following four modes can be selected according to the combination of

the frequency division values of the main and reference dividers.

Mode

Main divider

Reference divider

A-0

15 bit

1024 fixed

A-1

14 bit

512 fixed

A-2

15 bit

640 fixed

A-3/4

15 bit

512 fixed