Multilayer capacitor doubles as varactor

Posted on Aug 11, 2012

The circuit is also an inexpensive VCO (voltage-controlled oscillator) with only five components. Many types of ceramic capacitors for surface-mount placement are on the market. The parts become continually smaller because of space problems on the board, and the capacitance values continually increase to compete with more expensive tantalum-electrolytic units. Unfortunately, capacitors with X5R, Z5U, or Y5V dielectrics have some undesirable properties.

Multilayer capacitor doubles as varactor
Click here to download the full size of the above Circuit.
Multilayer capacitor doubles as varactor - image 1
Click here to download the full size of the above Image.

They exhibit voltage-dependent capacitance values. The idea behind the circuit in Figure 1 is to check the influence of a dc bias voltage on the frequency of a simple oscillator. The net result is a low-frequency VCO with a relatively large voltage-gain figure, which depends largely on the type of capacitor you use.

The circuit is a simple oscillator using a Schmitt-trigger inverter. The frequency is a function of R1, C1, and C2. C2 is the ceramic capacitor with voltage-dependent capacitance. Using the value of C1, you can shift the frequency independently of C2.

This design uses a stable-foil-type capacitor for C1 to avoid bias-voltage-dependent effects in the measured results. If necessary, you can compensate the temperature coefficient of the capacitor with a combination of NTC, PTC, and metal-film resistors for R1. For measurements, this design uses a simple metal-film resistor. The capacitance change with temperature is normally less than 10% from 10 to 35°C for Z5U and Y5V and much lower for X5R.

Figure 2 shows the measured voltage-versus-frequency graphs with different values and types for C2. For Figure 2, C1=10 µF; the orange curve represents a 4.7-µF, 10V, Z5U multilayer capacitor, and the purple curve represents a 10-µF, 10V, Z5U multilayer capacitor.

Leave Comment

characters left:

New Circuits



Popular Circuits

220V Mains Quality Monitor
0.1Hz to 10Hz RF reciever
Audio notch filter 2
peak detector
PWM Speed Rotation Forard-Reverse and Regenerative Braking
Solar power related schematics
GPS reference clock NTP server with Gentoo
Reference earphones
Ceramic Resonators
Play Games with Nixie Tubes
Power Control
Double astable multivibrator circuit diagram
Cycle 100 MHz frequency counter circuit diagram
Multiple waveform generator circuit diagram