Rf oscillators, diode mixers, and frequency multipliers.
This section contains several types of circuit blocks for simulation with LTspice.
These include oscillators, FM oscillators (frequency modulation), frequency multipliers, and diode mixers.
Firstly you have to download and install LTspice from www.analog.com,
Then click on the names below to download the circuits and get LTspice to open the circuits
Regarding text on the circuit diagrams, blue text is just comment, black text is read by the spice simulator.
There is comment text on the circuits explaining how to run the simulation and plot the waveforms
in case of difficulty downloading, here are the circuits in this section as a ZIP file.
![The circuits in this section as a ZIP file.]()
Colpits Oscillator circuits
![Colpits oscillator, fixed frequency.]()
![Colpits oscillator, FM staircase voltage input, test.]()
![Colpits oscillator, FM 1khz audio input]()
Diode mixer circuits
In these Diode mixer circuits, the local oscillator operates the diodes as switches, either on or off.
You can think of this on/off waveform as a square wave, this means that the local oscillator consists of its fundamental frequency
and also a load of undesired harmonics at 3, 5, 7, 9 etc times the fundamental frequency, in a real circuit these extra frequencies would be filtered out.
The simplest ( 1 diode) mixer has the undesired characteristic that as well as the desired output, both of the input frequencies appear at the output.
you can stop the inputs from appearing at the output by using the more complex ( 2 diode, or 4 diode) mixers.
![4h single diode mixer,......... output is mixer output and both input frequencies]()
![4jj two diode mixer,........ output is mixer output and one input frequency]()
![4m 4 diode mixer,....... output is mixer output without either of the input frequencies]()
Frequency multiplier circuits
This type of circuit operates by distorting the signal,
either by overdriving and hence clipping the signal against the voltage rails, or some other method of clipping the signal.
This generates harmonics, a bandpass filter is then used to select the desired harmonic.
![4e freq multiplier]()
After a few circuits you may be able to ignore the directions written on the cct diagrams, as LTspice is reasonably simple to operate.