CMOS low power current source with reduced circuit complexity

Abstract

The paper describes the efficient CMOS technology based current source for system identification and it's layout realization with reduced circuit complexity. Square wave excitation current is preferred in energy constrained and embedded environment. It has been shown that by shortening the square waves, spectral purity of the excitation signals can be drastically improved. Further improvement can be achieved by introducing limited number of additional equally spaced current levels. The basic idea of such a solution is that by suitably adding several simple shortened pulses together some of the high energy harmonics are either further reduced or eliminated. This multilevel signal can be easily generated digitally and it enables simpler digital processing involving only additions and shifting. On the other hand required extra circuitry for multiple current levels should not eliminate main advantages of square wave excitation, such as reduced complexity and low consumption. Proposed solution improves the power consumption and reduces the complexity of the system as a whole compared to more generic approach. The current source output will be the shortened multilevel square wave signal. The output current value can be selected from range from 5 to 100 μA. The main advantage of this method is greater efficiency because for measuring cycle only one or two pairs of switchable current mirrors will be activated to drive the H-bridge.