DC coupling vs AC coupling

DC coupling allows both AC and DC signals through, while AC coupling accepts only AC signals.


Issue in AC coupling:  AC coupling rejects DC component in the signal, making

the average value of the signal to zero. 

Case 1: Waveform has 50% duty cycle, the peak value in both positive and negative cycles will be same. 

Case 2: Waveform doesn’t have 50% duty cycle.

After AC coupling, (average value is zero)

Area under the positive half cycle = Area under negative half cycle.

But the peak value for positive and negative half cycles will not be same.


Example:  Consider a square wave with duty cycle 1/3 and peak-to-peak value 3V.

After AC coupling, the peak values would become 2V, -1V respectively.

If the AC coupled device detects 1.5V as logic high,

-1.5V as logic low,  due to the above effect, there would be erroneous detection.


9 thoughts on “DC coupling vs AC coupling

  1. It is best comparison between ac and dc coupling. It is straight and easy to understand. The vs makes it attractive. Please tell me how I can read these journals.

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  4. Your analysis of the example is incorrect. Peak-to-peak of 3V means the voltage swings from +1.5V to -1.5V. If you assume +1.5V is “on” and the duty cycle is 1/3, this means that for 1/3 of the signal period time the device will be +1.5V and for 2/3 of the time period the device will be -1.5V.

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