why input signal amplitude is not specified in class d amp?

Hi,
I have a question on the class d audio amplifier. For the commercial class d amp product, i found there is no input signal amplitude specifications. E.g., for the output power spec, it is measured with the below condition:

THD+N=1%, VDD= 3.6V f=1kHz, RL=8Ω Pout=0.64W

For the above test condition, the amplitude of input 1KHz signal is not specified, is that mean we increae gradually the input signal amplitude from 0, and monitor the THD+N, untill it reached to the 1%, then we got the Pout at this condition, right?

Same question is for the THD+N measurement, increase the input signal amplitude and monitor the THD+N untill the Pout reached to 1W.

I wonder why not we specified the input signal amplitude and monitor the Pout and THD+N? That seemed more naturally for the design.

Thanks for the help.

Basicly, there is no specified input voltage conditions of Audio AMP whatever Class AB or D in datashhet. becasue the THD+N vs Po plot is almost same even with different input level. However THD+N will become a slight worse with increasing gain, at same output power, that is to say, if the input voltage gets samller, the THD+N will become a little worse reaching same power.

Re: why input signal amplitude is not specified in class d a

Most of the time, audio signals are very small, with less than 1V as the input and always several hundred mV or several tens mV, so there is no need to specify input range, also, there is always a PGA to amplify the incoming signals. For SNR testing, one may input a 1mV (-60dB) signal to test the performance, or input a 1V sine wave to test the performance

Re: why input signal amplitude is not specified in class d a

peterwangyu said:

Basicly, there is no specified input voltage conditions of Audio AMP whatever Class AB or D in datashhet. becasue the THD+N vs Po plot is almost same even with different input level. However THD+N will become a slight worse with increasing gain, at same output power, that is to say, if the input voltage gets samller, the THD+N will become a little worse reaching same power.

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Hi peterwangyu,
Thanks for the reply. Your reply is helpful to me, but leads to my other two questions.

1. "The THD+N vs Po plot is almost same even with different input level. " Does the differnt input signal level means different output power?

2.Since there is no specified input voltage conditions of audio amp datasheet, in designing/simulations, how should I set the input signal signal to simulate the THD+N for a good comparation with datasheet? Infact, this leads to my above 1st question, i.e., what the realtionship between the input signal level and the output power?

Thanks