A SPICE macromodel for the transient analysis of lossy dispersive coupled GaAs interconnect line system is considered. The model is based on finite Fourier integral transform in spatial domain and is used to the study the transient nature of the signals, signal delays, distortions and crosstalk in IC interconnections in digital integrated circuits. An equivalent circuit model is derived from the resulting nonlinear differential equations and is implemented as a macromodel in a general purpose circuit simulator, SPICE. The model provides an easy method of including skin effect and dispersion of the lines. This macromodel is an alternative method to the multiple PI or Tee sections lumped element modeling of distributed systems. The simulation times and accuracy are well compared to the reduced order PI section lumped element models.
A model on alpha-power law MOSFETs based source-coupled differential pair (SCDP) is discussed and a simple design procedure for realizing a linear CMOS SCDP transconductance element is proposed. The proposed or modified SCDP circuit using this procedure is an alternative to that of conventional SCDP and the circuit discussed has superior linearity for a wide range ±(0-300mv) of input differential voltage at a supply voltage of 1.2v. The modified SCDP also includes the circuitry needed to suppress the variation in the quiescent current with respect to input common-mode voltage noise. The SPICE results are used to verify theoretical predictions. The results show close agreement between the predicted model behavior and the simulated performance. The simulated result on Total Harmonic Distortion (THD) shows that the modified SCDP circuit is better than the conventional SCDP by about four times at input differential voltage amplitude of ±100mv. An example circuit, a second order continuous time gm-C band-pass filter is constructed using the fully differential modified SCDP and the fully differential conventional SCDP circuit and the result shows that the modified transconductor circuit is better in linearity (THD) than the conventional SCDP by about two times at the input differential voltage amplitude of ±100mv. An automatic digital compensation scheme for temperature is also presented and the temperature coefficient of output current is reduced by about eight times to 250ppm/deg.C after compensation for the maximum change in temperature of 150deg.C and at the input differential voltage of 100mv.
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