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CXA1695L

(1) VHF oscillator circuit

The differential oscillator circuit with Pin 11 output and Pin 9 input.

Connect an LC resonance circuit comprising a varicap diode to Pin 11 through a coupling capacitor. The

positive feedback from the resonance circuit is applied to Pin 9 through a feedback capacitor to execute

oscillation. Note that if a parasitic capacitance across Pins 9 and 11 is too large, it may cause undesired

oscillation.

(2) VHF mixer circuit

This is a double-balanced mixer having small leakage of local oscillation signal. The RF signal input

terminal are Pins 2 and 4. In normal use, the signal is input to one pin while the other pin is connected to

GND by decoupling capacitor. The RF signal is converted to IF with the signal supplied from oscillator.

The converted RF is sent to the IF amplifier and output to Pins 3 and 5 simultaneously.

(3) UHF oscillator circuit

This is the differential oscillator same circuit as the VHF oscillator. In Electrical Characteristics Test Circuit,

oscillation is executed as a Colpitts oscillator using one side transistor of the differential amplifier.

(4) UHF mixer circuit

This is the double-balanced mixer same circuit as the VHF mixer. The RF signal input terminal are to Pins

10 and 12.These are used balanced differential input from pre-stage double tune circuit, or an unbalanced

input to Pin 10 with the capacitor connected at Pin 12 to GND. Balanced input achieves better NF rather

than unbalanced input.

Otherwise, the conditions and usage are the same as for the VHF mixer.

(5) IF amplifier circuit

The mixer output signal is amplified by the IF amplifier and output to Pin 1. The output impedance is

approximately 75

Ω.

(6) UHF/VHF switching circuit

UHF / VHF modes are switched by the DC voltage at Pin 7. UHF operation is for open or 0V; VHF

operation, for 3V or more.

Normally, for internal protection UHF/VHF switch is performed by 9V or open through about 10k

Ω resistor.

Notes on Usage

Care should be taken in placing external parts because high frequencies are present. Adjust accordingly

to prevent heat problems with special care for Pins 6 and 13 (GND) whose heat dissipation accumulate.