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I'm presuming you want to transmit digital data to a receiver, as long as the frequency is high enough to carry the data it will work. Technically the lowest frequency is twice the data rate so in most cases a few tens of KHz is enough. There is no upper limit.
Yes, my intention is to transmit digital data. So for instance, if the transceiver frequency is around 2.45GHz roughly what is the minimum ADC frequency?
The ADC is not part of the transmitter, a full custom CMOS transmitter had been designed in the range of ISM band of around 2.4GHz and 2.5GHz. A full custom CMOS sensor had also been designed which has analogue output. My job is to design an ADC to combine the sensor and transmitter together. I hope you understand my explanation.
Yes, that had been already betwixt's guess. But the requirements for the ADC sampling rate and other parameter will be set by intended measurement speed and resolution.
Yes thank you FvM for your suggestion, but my most concern is (as my question in the first post) does the transmitter radio frequency take some effect (constraint) on my ADC design? This question had been answered by Brain (thank you Brian).
So my second question is if the frequency of the transmitter is 2.4GHz - 2.5GHz, what is the minimum frequency for the ADC?
There is no minimum frequency. Apart from the requirement to be able to carry the data rate, the ADC and frequency are unrelated. At 2.4GHz you are already many times higher in frequency than most ADC circuits will produce. A lower ADC rate simply means it takes longer to convert a voltage to a number, it doesn't directly depend or constrain the transmitter frequency.
You need to be concerned with the baseband rate, not
the carrier frequency. However for compliance you may
find it desirable to piggyback on one of the existing clock
or IF frequencies so as not to add another harmonic-series
to the soup. Like in cell phones you can do almost anything
you want on a 13MHz or 26MHz clock because everybody
expects trash there. Similarly whatever the baseband data
rate clock is, has to be expected in the spectrum already.
Hide behind the fat kid. And try not to be fatter.
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