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CXA3025N

Description of Operation (See Electrical Characteristics Measurement Circuit.)

VHF oscillator circuit

This is a differential amplifier type oscillator circuit with an output at Pin 15 and an input at Pin 13.

Connect an LC resonance circuit comprising a varicap diode to Pin 15 through a coupling capacitor, and input

the positive feedback from this resonance circuit to Pin 13 through a feedback capacitor to execute oscillation.

Note that if the capacitance across Pins 13 and 15 is too large, positive feedback may be applied via a

parasitic capacitance causing undesired stray oscillation. The resistance connected to Pin 13 is for preventing

parasitic oscillation, and is inserted to ensure stable oscillation.

VHF mixer circuit

The mixer circuit adopts a common emitter type double-balanced mixer with little leakage of the local

oscillation signal. The RF signal is input to Pins 8 and 9. During normal use, the RF signal is input to one pin

while the other pin is connected to GND. The RF signal is converted to IF frequency by the signal supplied

from the oscillator and then output to Pins 4 and 5.

UHF oscillator circuit

The UHF oscillator is formed from two collector-grounded Colpitts oscillators, and oscillation is provided at the

differential input through an LC resonance circuit comprising a varicap diode. An LC resonance circuit

comprising a varicap diode is connected across Pins 16, 17, 20 and 21.

UHF mixer circuit

Like the VHF mixer, the UHF mixer adopts a double-balanced mixer. The RF signal is input to Pins 11 and 12.

There is a balanced input at the differential from both edges of the secondary coil of the pre-stage double tune

circuit, or an unbalanced input to Pin 11 with a capacitor connected at Pin 12 to GND. Otherwise, the

conditions and usage are the same as those for the VHF mixer circuit.

IF amplifier circuit

The signal frequency converted by the mixer is output from Pins 4 and 5, and input to IF input pins 1 and 2

through an external IF tune circuit. For the IF tune circuit, a single tune circuit like the electrical characteristics

measurement circuit or a double tune circuit can be connected. The signal amplified by the IF amplifier is

output from Pin 24. The output impedance is approximately 75

Ω.

Also, the input block of the IF amplifier has a built-in coupling capacitor, and direct connection with the mixer

output is possible.

U/V switch circuit

UHF operation is chosen by applying voltage of 3V or more to Pin 23; VHF operation for 0V or OPEN.

PLL oscillator signal output circuit

The oscillation signal is output to Pin 22 (PLLOUT) through a buffer amplifier. The resistance connected to the

output pin is used to adjust the current flowing to the buffer amplifier. The resistance value is adjusted

depending on the connected load, and output distortion can be minimized.

Notes on Operation

Care should be taken for grounding, etc. when placing external parts as high operating frequencies are

present. In addition, since the GND pins (Pins 6, 7, 18 and 19) also serve as heat dissipation pins, care should

be taken to prevent heat problems.

Care should also be taken to prevent electrostatic damage to high frequency I/O pins.