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Question about Frequency Tripler Circuit Using Complementary Transistors Pair


Hello everyone,

I'm an electronics hobbyist currently learning about microelectronics. I've been trying to understand this Frequency Tripler circuit (image below) operates, particularly on how the transistors go to saturation. From the oscilloscope readings (yellow trace for Vin and blue trace for Vout), I could see that Q2 (NPN) reaches saturation during the positive cycle of Vin, and Q1 (PNP) reaches saturation during the negative cycle of Vin.

What I don't understand is how each transistor goes to saturation once at the time and not both, especially when Vbe for Q1 is always negative and Vbe for Q2 is always positive? When I measured the base currents, I notice that:
- During the positive cycle of Vin, ~130uA went into the base of Q2 and only ~3uA went out the base of Q1.
- During the negative cycle, ~3uA went into Q2 and ~130uA went out of Q1.

Why aren't the base currents more or less the same if both transistor are conducting?

This is my first time posting here so I apologize in advance if I made any mistakes in my post. Please let me know if there are ways I can make my question clearer. Thank you for your help!

Because basically (heh) speaking, NPN conducts when current are pushed into its base and PNP conducts when current are pulled out of its base. Ergo the two transistors will never conduct at the same time, and base current will never be the same. Except at zero crossing when both are zero...

With this configuration there will also approx 2Vbe band near midpoint where base is positive but not positive enough to make NPN conduct, or negative but not negative enough to make PNP conduct. That what's causing the "dip". This circuit is basically exploiting the crossover distortion of a class B output. Just that I didn't expect the transition region to be this clean.

The transistors don't switch off, both conduct at the same time.  The circuit works by saturation limiting the output swing.

Its a high gain inverting amp but the saturation limits the swing relative to the input, so the swing direction reverse every time each transistor enters or leaves saturation.

That is a very interesting circuit.

If we fed the output to a comparator and reduce the input voltage amplitude to around 0.7v, then we will get a very decent tripler output waveform.

Wallace Gasiewicz:
Interesting...so I built the circuit.  There is a lot of phase difference in thethree peaks which can be varied by adjusting the V+ and V-.  Lots of Phase noise.


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