ADC/DAC Sample Rate and Reference Voltage

In summary: The sampling rate is actually 10 bits regardless of what Vdd is set to.In summary, the Microchip MCP3004 10 bit ADC can sample at a rate of 200 ksps when operating at 5V, or 75 ksps when operating at 2.7V.
  • #1
tomizzo
114
2
I am currently working on a circuit design that is featuring both a ADC and DAC. I'll focus my question on the ADC in this thread.

I'm trying to figure out what each pin does. Am I correct in assuming that the Vref pin on the an ADC chip is used as the maximum encoded value for a voltage? Say for example I have an ADC capable of encoding a 0-5V signal with 8 bits of resolution. And then say that I only want to be measuring a maximum voltage of 2V. If I were to tie 2V to the Vref pin, this should scale the encoded values 0-255 to correspond with voltages from 0-2V. Correct?

However, I noticed on a recent data sheet that the sample rate of the ADC is dependent on the value of Vref (see image below). Why is this? Why would the sample rate depend on what is set to the Vref pin?

Any help regarding this?
 

Attachments

  • Capture.JPG
    Capture.JPG
    75.9 KB · Views: 552
Engineering news on Phys.org
  • #2
The reference voltage is the maximum value for the conversion as you correctly thought. The rate then would be determined by the size of each chunk of from the 8 bit value. i.e. Vref/256
 
  • #3
dlgoff said:
The reference voltage is the maximum value for the conversion as you correctly thought. The rate then would be determined by the size of each chunk of from the 8 bit value. i.e. Vref/256
Could you expand on why the sample rate is dependent on the value of Vref? Or is the data sheet saying that the sample rate is actually dependent on the value of Vdd which just happened to be the same as Vref?
 
  • #4
That's weird. It's not obvious why the sample rate would depend on Vref. I could see it depending a bit on Vdd, but not Vref.

Which chip is it?
 
  • #5
berkeman said:
That's weird. It's not obvious why the sample rate would depend on Vref. I could see it depending a bit on Vdd, but not Vref.

Which chip is it?

It is a Microchip MCP3004 (data sheet: http://ww1.microchip.com/downloads/en/DeviceDoc/21295d.pdf).

The more I look at this, the more I'm starting to assume that the sample rate is dependent on the value of Vdd and not Vref. They simply were listing an example in which case Vdd would be 5.0V or 2.7V in which case the maximum Vref would also have to be 5.0V and 2.7V respectively.
 
  • #6
Yeah, that would make more sense. And that's how it's listed in the opening bullets of the datasheet:

• 200 ksps max. sampling rate at VDD=5V
• 75 ksps max. sampling rate at VDD=2.7V

:-)
 
  • #7
But it's a 10 bit ADC. Wouldn't it be faster with 8 bits as opposed to 10 bits? Assuming the same clock rate.

Edit: Okay. Disregard this. I see my mistake. It is VDD that "determines" throughput.
 
Last edited:

1. What is the significance of sample rate in ADC/DAC?

Sample rate refers to the number of samples taken per second by an ADC (analog-to-digital converter) or DAC (digital-to-analog converter). This rate determines the resolution and accuracy of the converted signal.

2. How does the sample rate affect the quality of the signal?

A higher sample rate results in a more accurate and detailed representation of the original analog signal. This is because a higher number of samples can capture more information and reduce the amount of distortion and noise in the digital signal.

3. What is the ideal sample rate for ADC/DAC?

The ideal sample rate for ADC/DAC depends on the specific application and the desired level of accuracy. In general, a sample rate of at least twice the highest frequency component of the signal (Nyquist rate) is recommended to prevent aliasing and ensure accurate signal reconstruction.

4. What is the reference voltage in ADC/DAC and why is it important?

The reference voltage in ADC/DAC is the voltage against which the analog input is measured. It is important because it determines the dynamic range and resolution of the converted signal. A higher reference voltage allows for a larger range of analog input values to be accurately represented in the digital signal.

5. Can the sample rate and reference voltage be adjusted in ADC/DAC?

Yes, the sample rate and reference voltage can be adjusted in most ADC/DAC systems. However, it is important to carefully select these parameters to ensure accurate and reliable signal conversion for the specific application.

Similar threads

16 bit sigma delta ADC question
    • Electrical Engineering
Replies
22
Views
6K
Can Linux Improve ADC Sampling Rate on Intel Galileo Gen 2?
    • Electrical Engineering
Replies
7
Views
4K
How can I increase the sampling rate for AnalogRead() on Arduino Uno?
    • Electrical Engineering
Replies
1
Views
1K
Window Comparator: Understanding the Output Behavior and Common Errors
    • Electrical Engineering
Replies
5
Views
2K
Ht12e/d input output logic question
    • Electrical Engineering
Replies
2
Views
1K
Logic outputs to logic inputs of devices with different Vcc
    • Electrical Engineering
Replies
13
Views
1K
Monitoring Voltage of Batteries w/ ADC0834 - Help Needed!
    • Electrical Engineering
Replies
4
Views
4K
Is resolution strictly defined in volts?
    • Electrical Engineering
Replies
19
Views
3K
TFT LCD Display - where is the circuitry?
    • Electrical Engineering
Replies
11
Views
7K
Successive Approximation ADC Question
    • Engineering and Comp Sci Homework Help
Replies
10
Views
3K

Hot Threads

Recent Insights

Back
Top