Intro
As part of the Analog Discovery 3 road test, I want to show examples of using both its waveform generator and its oscilloscope at the same time with a real circuit.
This example uses an TI LM2907 (developed by National Instruments before they were acquired by TI) frequency-to-voltage converter chip. I used the Digilent AD3 to generate various frequencies for the circuit to convert to voltages, actually I used the sweep function of the AD3 to continuously sweep the frequency from 5 Hz to 1 KHz.
I also wanted to see what the frequency response of the circuit is. To do this I created a step change in frequency to see how long the circuit takes to respond. Then I increased the modulation frequency until the circuit's response decreased to 50% of its maximum amplitude. This gave a measure of the circuits bandwidth to measure frequency changes.
F to V Circuit Demo
Schematic
VO = VCC × fIN × C2 × R1 × K
This formula indicates the output voltage is proportional to both capacitance and frequency, so if C2 is constant the output is proportional to the input frequency and if the frequency is constant, the output is proportional to C2.
Discussion
The Analog Discovery 3 Is very useful in experimenting with circuits like this where the circuit may need a variable frequency input and you want to see the waveforms at various places in the circuit.
The user interface is different from other instruments and there are many features to understand, but adjusting settings with a mouse and keyboard is quick and easy. Finding the bandwidth of an analog frequency to voltage converter like this could be quite an exercise with traditional instrumentation, but with the AD3 it can all be done with one instrument.
Links:
Pretty Cool Raster Text Display on an AD3
AD# - Frequency-to-Voltage Converter
AD3 - Capacitance-to-Voltage Converter
Digilent Analog Discovery 3 Road Test
