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Voltage Controlled Oscillator (VCO)

The resistors around the input are designed to ensure that the positive and negative integration times are identical, hence R3A and R3B in parallel because the exact half value isn’t available in most resistor series. Sensitivity is halved because the effective supply voltage has been doubled compared to the single supply version shown in Figure 2.

This is the frequency obtained when there is no external modulation. The frequency change is related to the amplitude, and the rate-of-change is determined by the modulation frequency.

Fully temperature compensated circuitry is required if you need a precision VCO, and if that’s what you need then this general class of VCO is not suitable. The next circuit will do just that, but it’s not a precision circuit.

Message 2 of 7. Despite appearances, the input will not be at zero volts when the pot is centred.

By clicking “Post Your Answer”, you acknowledge dqtasheet you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies. I’ve included it here purely for the sake of completeness and to show how easy it was to make a VCO a few years ago.

The circuit diagram of a voltage controlled oscillator using LM is shown in the figure below. It will work with as little as 50mV input, but will become very non-linear and somewhat unpredictable. The LM IC can be operated from a single supply or dual supply.


National Semiconductor LM Series Datasheets. LMCN, LM, LMC Datasheet.

There aren’t many dataseet either. Most Active Software Boards: Thus by varying the voltage across the varicap diode in the tank circuit, the output frequency of the VCO can be varied.

This is engineering, not poetry. There will be some non-linearity, and the figures are intended as a guide only. Voltage controlled oscillator is a type of oscillator where the frequency of the output oscillations can be varied by varying the llm566 of an input voltage signal.

I did find a datasheet The input can be driven from a ramp waveform or manually, and it’s not at all difficult to obtain a Figure 4 – Diode Sinewave Shaper. Figure 5 – Frequency Modulated Sinewave Output. FiddyOhm first of all i’m sorry my english isn’t that goodwhat i meant was the frequency keeps changing even though the control voltage is constant i haven’t even started to vary it yet.

The block diagram of a typical voltage controlled oscillator is shown below.

A voltage controlled oscillator VCO isn’t something you need every day, and you may never have thought that you need one at all. C1 is selected to give response down to the lowest frequency of interest, and is less than 1. The base frequency can be dafasheet by a pot as shown, and the modulation signal is symmetrical around zero volts.

The frequency modulation is clearly visible, as is the wave shape. Your email address will not be published. Linear voltage controlled oscillators are generally used to produce a sine wave.


It’s important to connect the input stage including the transistor as shown. Thank u very much.

LM566 Datasheet

Using a ground reference for the input stage of a dual supply version also means that the modulating voltage AC, DC or a combination of the two must always be positive. In such oscillators, an LC tank circuit is used pm566 producing oscillations. In most cases, this km566 a serious limitation, but expecting low distortion isn’t an option – the best you can expect is around 1.

Some advertise them for insane amounts of money Can you recommend a circuit or teach me how to do this? This will change slightly depending on the load and the ICs internal temperature. However, there’s not really a great deal of benefit to using a dual supply, as it doesn’t simplify the circuit in any way. The circuit as shown expects an input voltage of around 8V peak-peak, as will be obtained from the circuit shown in Figure 3. The output level and distortion will change with temperature.

LM datasheet & applicatoin notes – Datasheet Archive

The maximum frequency is also limited, so these circuits can’t be used for RF applications. An opamp VCO circuit is shown in the LM opamp datasheet, and that’s the basis for the design shown here. However, the supply voltage must be regulated, or the amplitude of the two outputs will vary with the supply voltage. The figure of Hz above applies only when the modulation signal is capacitively coupled as shown, and allows for the LM Frequency deviation problem Ask Question.