Capacitive cancellation technique in design of CMOS low noise amplifier for ultrasound applications

In this paper active capacitive cancellation technique, is proposed for alleviating the side effects of the parasitic capacitance of the ultrasound piezoelectric probe and cable. This parasitic capacitance imposes a low frequency pole at the input of the circuit, which deteriorates the noise and the transient response of the circuit, crucial parameters for ultrasound imaging systems. Employing a capacitor in a positive feedback loop of a well-defined gain amplifier actively cancels the parasitic capacitance at the input of the amplifier. Making use a binary weighted capacitor bank keeps the circuit safely away from the instability problems due to the variations of process and corner cases. For verification of the proposed technique, the circuit was designed and simulated in a 0.18 A mu m, 1.8 V CMOS technology. Simulation results show that this technique for equal power consumption presents a better noise performance and more than 100% higher bandwidth compared to the conventional active resistive termination approach.