how to determine Full scale range for ADC.

[Ranand]

Hi ,
How does one determine the full scale range for the ADC when it is specified in terms of Vrms?

Can I compute the Full scale peak value as Vrms*2*sqrt(2) ?
Also does this mean that the ADC is single ended? If not, how does one determine the lowest input voltage?

The spec is as given in the attached image



Thanks,
Ranand

 

[crutschow]

The peak voltage would be Vrms * sqrt(2).
The lowest input voltage is determined by the resolution of the ADC (number of bits)

 

[Ranand]

Sorry for not being clear enough , I wanted to know the full scale voltage range for the ADC .Will it be 0 to Vpeak or -Vpeak?


Thanks,
Ranand

 

[KlausST]

Hi,

you can not use sqrt(2). Except for pure, undistorted sine.


Your specification picture seems to me like an audio device.
For audio input i recommend to use at least +/- 3 x VRms.

audioguru should have good experiece on that. Maybe he can give you more information on that.

If you don´t use it for undistorted sine or audio, then pleas give more information.
*********
Wheter you need single ended or not depends on your input signal.

*******
RMS to peak:
DC: peak = RMS
50% duty cycle unipolar PWM: peak= 1.414 x RMS
50% symmetrical square wave: peak = +/- RMS
sine: peak = +/- 1.414 x RMS
audio: is an undefined mixture of many various frequencies, therefore it is hard to tell


Klaus

 

[Ranand]

Thanks for your clarification Klaus!

I am trying to model a simple audio codec(PGA , ADC and DAC) based on the TLV320aic23b specs. I have been looking into

I found it difficult to interpret the input signal values from the datasheet for the PGA(Programmable Gain Amplifier) and the ADC. The only specs I could figure out were the Analog operating range(Avdd+/-0.3) and variable gain values.Also I am not able to figure out if the PGA and ADC will be single ended or differential from the datasheet.
Can you please help me with the specs like input range for both?

Thanks,
Radhika

 

[KlausST]

Hi,

Inputs: RLineIn, RLineIn (single ended)
Output: ROut, LOut (single ended)

max input voltage: -0.3V ... AVDD +0.3V, non destroying,
The inputs are biased to VMid. There is a input circuit recommendation.

But the full scale values in the datasheet are strange.
in note3 they refer to a 1kHz sine signal. then the 0dB = 1V RMS makes sense.

But how to interpret (2.3.2.1 Line output) "0-dB full-scale output voltage (FFFFFF) = 1.0 VRMS" is not clear.
FFFFFF is the most positive DC output voltage. i doubt it is 1.0V DC.
(or -not likely- the minimum possible negative DC output voltage)

If you have a TLV320 by hand: test this.

************
Maybe interesting for you: ADAU1701. Evaluation kit available. PC software (graphical programming software), USB configurable, easy to use.
I tested it and it was funny how fast one can "configure" a lot of different applications. (filters, mixers, delay, effects, crossover...)

Klaus

 

[Ranand]

Thanks for your help Klaus,

I do not have the option to test the TLV320 in hardware.
I had a few questions,
what do you mean by non destroying for the analog input voltage?
Also does the max input voltage range of -0.3 to (3.3 +0.3)V indicate that the ADC inputs can vary between -0.3 to 3.6 V or should I consider it to vary between 0 to 1Vrms(1.414Vp)? How does one interpret this spec?


(2.3.2.1 Line output) "0-dB full-scale output voltage (FFFFFF) = 1.0 VRMS" is for the DAC , so could it indicate that the anlog output of 1Vrms will correspond to the Fullscale input of FFFFFF to the DAC?


Thanks,
Ranand