How to make a voltmeter in FPGA

[david90]

how do u make one?

 

[Big Boy]

voltmeter fpga

Just need an ADC. For an FPGA-only (no external analog to digital converter), with minimal external component, see Xilinx app note XAPP155

**broken link removed**

 

[david90]

delta sigma fpga

how does the ADC work? Say u have a sin wave and it was converted to digital. how would it look in digital?

 

[Big Boy]

Re: voltmeter in fpga

ADC simply convert an analog signal to digital numbers by measuring it's amplitude at any giver time.

So, for example, suppose your ADC work at 20KHz. This meen that 20 000 times per seconds, the ADC will take the voltage at input, and output a value corresponding to that voltage level at that instent.

ADC also have an input range, and specific number of bits. Let's suppose the ADC is 8-bit, and have a range of 0~2.55V. This meen that at 0V, the ADC will output 0. And at maximum of 2.55V, the ADC will output 255. Within those 2 bounds, the ADC will output a value that is proportional to the voltage level, in a linear fashion (i.e. will increase output by 1 each time the input increase by 0.01V).

The number of bits of your ADC will tell the number of steps it can give. For example, a 10-bit DAC will have 4 times more possible value than 8-bit DAC.

Last thing is that you usually can't configure the input range. For example, a 10-bit DAC that have a range of 0~4.095V can not be fed 5V directly. So, if you wish to measure voltage between -100~+100V (for example), then you need to provide input circuitry that will level the voltage to the ADC input voltage range.

In the case of XAPP155, the ADC is formed by using an analog comparator. One input is your input signal, the other input is the output of a delta-sigma DAC coded in the FPGA (DAC being the inverse of ADC). The input range is the output voltage range of the FPGA DAC part (something like 2.5V or 3.3V for example, depending on the IO standard used). Number of bits precision is determined by the delta-sigma DAC number of bits.