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Project Notes

#378 BJT Phase Splitter

Simple unity-gain phase splitter in a little breadboard-compatible package.

Build

Notes

Section 2.08 in the The Art of Electronics describes a unity-gain phase splitter which generates an output signal and its inverse (180˚ out of phase). This is achieved with a common emitter amplifier with emitter degeneration for a gain of -1 (~ 4.7kΩ/4.7kΩ)

With an input signal of 100kHz, the input coupling capacitor should be greater than 39pF - I’m using 100nF here.

Testing

In the following tests, the scope is connected as follows

  • CH1 (yellow): SIGNAL input, DC coupled - 100kHz 1v peak-peak sine wave
  • CH2 (blue): SIGNAL- inverted output, DC coupled, offset varies according to Vcc
  • CH3 (red): SIGNAL+ non-inverted output, DC coupled

PhaseSplitter_test

Vcc=5V

With VCC=5V, the quiescent point:

  • non-inverting output centered around 0.8V
  • inverting output centered around 4.3V

CH2 (blue) is offset -2V

scope_100khz_5v

Vcc=9V

With VCC=9V, the quiescent point:

  • non-inverting output centered around 1.9V
  • inverting output centered around 7.2V

CH2 (blue) is offset -4v

scope_100khz_9v

Vcc=15V

With VCC=15V, the quiescent point:

  • non-inverting output centered around 3.0V
  • inverting output centered around 7V

CH2 (blue) is offset -4v

scope_100khz_15v

Construction

Schematic

Testing on a breadboard:

Breadboard

PhaseSplitter_bb_build

I put on a piece of protoboard in a breadboard-compatible layout:

PhaseSplitter_build_layout

Build

Credits and References

About LEAP#378 BJTSignals
Project Source on GitHub Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.