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• This catalog has only typical specifications because there is no space for detailed specifications. Therefore, please review our product specifications or consult the approval sheet for product specifications before ordering.

1. Cautions for Designing Oscillation Circuits

As described in Chapter 2, the most common oscillation

varies with the application and the IC being used, etc.

Although the basic configuration of the circuit is the

same as that of a quartz crystal, the difference in

mechanical Q results in the difference of the circuit

constant.

This chapter briefly describes the characteristics of the

oscillation circuit and gives some typical examples.

It is becoming more common to configure the oscillation

circuit with a digital IC, and the simplest way is to use

an inverter gate.

Fig. 4-1 shows the configuration of a basic oscillation

circuit with a C-MOS inverter.

INV. 1 works as an inverter amplifier of the oscillation

circuit. INV. 2 acts to shape the waveform and also acts

as a buffer for the connection of a frequency counter.

The feedback resistance Rf provides negative feedback

around the inverter in order to put it in the linear

region, so the oscillation will start, when power is

applied.

If the value of Rf is too large, and if the insulation

resistance of the input inverter is accidentally

decreased, oscillation will stop due to the loss of loop

gain. Also, if Rf is too great, noise from other circuits

can be introduced into the oscillation circuit.

Obviously, if Rf is too small, loop gain will be low. An Rf

of 1MΩ is generally used with a ceramic resonator.

Damping resistor Rd provides loose coupling between

the inverter and the feedback circuit and decreases the

loading on the inverter, thus saving energy.

In addition, the damping resistor stabilizes the phase of

the feedback circuit and provides a means of reducing

the gain in the high frequency area, thus preventing the

possibility of spurious oscillation.

180°.

The proper selected value depends on the application,

the IC used, and the frequency.

X

Rd

INV.1

IC

IC

INV.2

Output

Fig. 4-1 Basic Oscillation Circuit with C-MOS Inverter

IC : 1/6TC4069UBP(TOSHIBA)

Rd : Dumping Resistor

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P17E.pdf

2012.10.31