A project log for Fully analog digitally controlled voltage source

Voltage is set with three BCD switches with a step of 10mV

klimaKlima 05/30/2023 at 22:050 Comments

An important feature of the circuits like the one designed (which is effectively a digital to analog converter) is maintaining the monotonicity.

It means, that for every change of set value to a value higher by one least significant digit, the output value also increases. Since I already had the simulation script, I simulated the voltage difference between consecutive steps:

Monotonicity of the circuit (simulation data)

 Every time the value drops below 0, the monotonicity is lost. It can be seen, that for some extreme combinations of component values within their specified tolerances, the monotonicity will be lost for transition from 7.99V to 8.00V. The ideal value (for ideal components) of change is 0.01V.

For my prototypes, the following values were measured:

Set value
Measured value Prototype #1
Measured value Prototype #2
7.99 V7.9854 V7.9791 V
8.00 V8.0010 V7.9898 V

The monotonicity is therefore maintained even for this nevralgic step for both prototypes.

Out of curiosity, I also checked how this plot would look like if I specified 1% resistors in the circuit:

Monotonicity of the circuit with worse accuracy resistors (1%) - simulation data

It can be seen that the possible loss of monotonicity is much more probable and more steps with possible loss can be observed.