CXA3250N Ver la hoja de datos (PDF) - Sony Semiconductor

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Fabricante

CXA3250N

All Band TV Tuner IC with On-chip PLL

Sony Semiconductor 

CXA3250AN

Description of Analog Block Operation

(See the Electrical Characteristics Measurement Circuit.)

VHF oscillator circuit

• This circuit is a differential amplifier type oscillator circuit. Pin 18 is the output and Pin 16 is the input.

Oscillation is performed by connecting an LC resonance circuit including a varicap to Pin 18 via coupled

capacitance, inputting to Pin 16 with feedback capacitance, and applying positive feedback.

• The amplifier between Pins 16 and 18 has an extremely high gain. Therefore, care should be taken to

avoid creating parasitic capacitance, resistance or other feedback loops as this may produce abnormal

oscillation.

VHF mixer circuit

• The mixer circuit employs a double balanced mixer with little local oscillation signal leakage.

The input format is base input type, with Pin 12 grounded via a capacitor and the RF signal input to Pin

13. (Pin 12 can also be used to switch the PLL mode according to the applied DC voltage value.)

• The RF signal is fed from the oscillator, converted to IF frequency and output from Pins 9 and 10.

UHF oscillator circuit

• This oscillator circuit is designed so that two collector ground type Colpitts oscillators perform differential

oscillation operation via an LC resonance circuit including a varicap.

• Resonance capacitance is connected between Pins 19 and 20, Pins 20 and 21, and Pins 21 and 22, and

an LC resonance circuit including a varicap is connected between Pins 19 and 22.

UHF mixer circuit

• This circuit employs a double balanced mixer like the VHF mixer circuit.

The input format is base input type, with Pins 14 and 15 as the RF input pins. The input method can be

selected from balanced input consisting of differential input to Pins 14 and 15 or unbalanced input

consisting of grounding Pin 14 via a capacitor and input to Pin 15.

• Pins 9 and 10 are the mixer outputs.

IF amplifier circuit

• The signals frequency converted by the mixer are output from Pins 9 and 10, and at the same time are

AC coupled inside the IC and input to the IF amplifier.

• Single-tuned filters are connected to Pins 9 and 10 in order to improve the interference characteristics of

the IF amplifier.

• The signal amplified by the IF amplifier is output from Pin 25.

The output impedance is approximately 75 Ω.

—17—

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