# Finding the input bit rate of an analogue input

Suppose I have 4 of 300bps synchronous digital input and 1 of analogue input with a bandwidth of 500Hz. The analogue input is sampled at 4bit using PCM. All the channels are multiplexed with TDM.

As one of the input is of analogue, I need to convert that to digital input first before TDM can be carried out. Since the analogue signal will be sampled at 4bits, my initial idea was to use the Nyquist sampling theorem to have 500Hz × 2 = 1000 samplings per second. But on a second thought, this is merely the bandwidth and I cannot do this unless it is said that the highest frequency is 500Hz.

However, then how should I find out the input bit rate of the analogue input channel for the TDM multiplexing?

## migrated from electronics.stackexchange.comNov 22 '11 at 13:08

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• You're not necessarily on the wrong track; under the right conditions, you can do something called bandpass sampling to sample at ~2x the bandwidth of the signal irrespective of its center frequency. – Jason R Sep 23 '11 at 14:01