Voltage to frequency conversion using VFC32

1. Voltage to frequency conversion using VFC32

Hi,

I am using VFC32 as Voltage to frequency. I want to make circuit that will convert 10 to 110 kHz signal in to 0 to 10V.
I was getting 10 kHz for 0V and 110 kHz for 10V but i didn't get linearity.
How to get linerity in VFC circuits.
Thanks.

Kartik patel  Reply With Quote

•

2. Re: Voltage to frequency conversion using VFC32

Hi,

Datasheet says it has good linearity.
Usually darasheets are correct.

We don't know your expectations regarding linearity.
We don't know how you measured your linearity and we don't know the measurement results.
We don't know your circuit.

You see we don't know much .... this makes it impossible to help.

Klaus  Reply With Quote

3. Re: Voltage to frequency conversion using VFC32

Hi,
Please find the attachment of the circuit I am using for voltage to frequency conversion.
I have set 10 kHz for 0V and 110 kHz for 10V. For the voltage between 1 to 9, I was getting some random frequency like 310 kHz for 2V, etc.
Also, the Behaviour of the practical circuit is not match with the theoretical calculation of Frequency output.

Fout= Vin/ 7.5 R1 C1

where; C1= One-shot capacitor(in my case 50 pF)
R1=Input resistor(in my case 50kΩ potentiometer)
Vin= Input voltage(0 to 10V)  Reply With Quote

•

4. Re: Voltage to frequency conversion using VFC32

50 pF doesn't fit your formula. It get > 200 pF.

Did you check the integrator and pulse output waveforms? How do you measure frequency?  Reply With Quote

5. Re: Voltage to frequency conversion using VFC32

I also would ask the question: How did you measure the frequency? With a frequency enabled DMM? With an oscilloscope?

You really, and I mean really require to show us the output waveform with an oscilloscope.
If you only measured with a DMM, there could be multiple noise pulses or glitches that could be faking the readings.

Ask me how I know.  Reply With Quote

6. Re: Voltage to frequency conversion using VFC32

Hi,
I am using Keysight DSO-X 2024A for frequency measurement.
Now I am getting linearity for 0 to 10VDC. I am getting 10kHz for 0 V and 110 kHz for 10V.

Fout= Vin/ 7.5 R1 C1

where; C1= One-shot capacitor(in my case 285 pF)
C2= Integrating capaciotor(909µF)
R1=Input resistor(in my case 40kΩ )
Vin= Input voltage(0 to 10V)
I am getting good linearity.

Can you suggest me components selection for Frequency voltage conversion?
Please find a circuit for a frequency to voltage conversion.  Reply With Quote

7. Re: Voltage to frequency conversion using VFC32

Now I am getting linearity for 0 to 10VDC.
Why now? What did you change?

C2= Integrating capacitor(909µF)
µF? Really?  Reply With Quote

•

8. Re: Voltage to frequency conversion using VFC32

[By calibrating the gain and offset potentiometer 50 k and 100 k respectively. ]Why now? What did you change?

µF? Really?[Yes; C2 as per the datasheet.

C2 (µF) =100/fFS; if fFS ≤ 100kHz; 0.001; if 100kHz < fFS ≤ 500kHz;
0.0005; if fFS > 500kHz or C2 = 10²/FMAX]  Reply With Quote

--[[ ]]--