  This paper presents a simple method for estimating the thermal noise voltage
variance in passive and active switched-capacitor (SC) circuits using
operational transconductance amplifiers (OTA). The proposed method is based on
the Bode theorem for passive network which is extended to active circuits based
on OTAs with capacitive feedback. It allows for a precise estimation of the
thermal noise voltage variance by simple inspection of three equivalent
circuits avoiding the calculation of any transfer functions nor integrals. In
this Part I, the method is applied to SC amplifiers and track&hold circuits and
successfully validated by means of transient noise simulations. Part II extends
the application of the method to integrators and active SC filters.
