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CXA3250N

All Band TV Tuner IC with On-chip PLL

Sony Semiconductor 

CXA3250AN

Description of Functions

The CXA3250AN is a ground 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 oscillation and IF amplifier circuits required for frequency conversion to IF, this

IC also integrates a PLL circuit for local oscillation 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 oscillation 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 oscillation frequency to the desired frequency. It consists of a programmable

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

supports both the I2C bus and 3-wire bus formats.

During I2C bus control, the frequency steps of 31.25, 50 or 62.5 kHz can be selected by the data-based

reference divider frequency division setting value.

During 3-wire bus control, these frequency steps can be selected by the combination of the communication

word length (18 or 19 bits) and the voltage applied to the BYP/MS pin.

5. Band switch circuit

The CXA3250AN has four sets of built-in PNP transistors for switching between the VL, VH and UHF bands

and for switching the FM trap, etc. These PNP transistors can be controlled by the bus data.

The emitters for these PNP transistors are connected to an independent power supply pin (VCC3) from the

oscillator, mixer and PLL circuits, and support either 5 V or 9 V as the RF amplifier power supply.

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