Noise analysis method for nonlinear circuits with two frequency excitations using the computer

This paper considers the noise in the nonlinear circuit, which operates by two signals i.e., the input signal and the periodic excitation (clock signal or carrier signal). These include the switched‐capacitor circuit and the mixer circuit. A method for the numerical analysis of the noise by a computer is proposed. The aliasing of the frequency component arises in such circuits, and the aliasing noise component over a wide frequency range must be considered in the noise analysis. In the proposed method, among the two excitations, the input signal is assumed as very small. The nonlinear circuit with only the periodic excitation is linearized around the periodic solution. Then a periodically time‐varying circuit is derived. An equivalent current source is connected in parallel with each noise source and its output noise is computed. Aliasing components folded back to the baseband from high‐frequency bands are calculated, and their powers are accumulated until their contributions become negligible. The proposed method is built into the circuit simulator SPREAD [1] and an experiment was executed. The usefulness of the algorithm was verified using a simple circuit, for which the strict solution can be calculated analytically. By the proposed method, the noise of the nonlinear circuit with two frequency excitations can be estimated at the design stage. This will greatly improve the productivity in the circuit design.