The sampling noise cancellation (SNC) technique has been applied to different discrete-time circuits in recent literature, but the cost of this technique has not been well studied. This paper gives a detailed analysis of the SNC approach in a track-and-hold amplifier (THA). Closed-form expressions are derived for each noise source in the THA during the sampling phase and are verified by simulations. The analysis shows that while the sampling noise can be cancelled, the noise from the extra amplifier and switches can become dominant and even outweigh the benefits from SNC. Therefore, the SNC technique should be used with attention to the trade-offs, as described in this paper.