Power MOSFET–Diode–Based Limiter for High-Frequency Ultrasound Systems

Abstract

The purpose of the limiter circuits used in the ultrasound imaging systems is to pass low-voltage echo signals generated by ultrasonic transducers while preventing high-voltage short pulses transmitted by pulsers from damaging front-end circuits. Resistor–diode–based limiters (a 50 Ω resistor with a single cross-coupled diode pair) have been widely used in pulse-echo measurement and imaging system applications due to their low cost and simple architecture. However, resistor–diode–based limiters may not be suited for high-frequency ultrasound transducer applications since they produce large signal conduction losses at higher frequencies. Therefore, we propose a new limiter architecture utilizing power MOSFETs, which we call a power MOSFET–diode–based limiter. The performance of a power MOSFET–diode–based limiter was evaluated with respect to insertion loss (IL), total harmonic distortion (THD), and response time (RT). We compared these results with those of three other conventional limiter designs and showed that the power MOSFET–diode–based limiter offers the lowest IL (−1.33 dB) and fastest RT (0.10 µs) with the lowest suppressed output voltage (3.47 Vp-p) among all the limiters at 70 MHz. A pulse-echo test was performed to determine how the new limiter affected the sensitivity and bandwidth of the transducer. We found that the sensitivity and bandwidth of the transducer were 130% and 129% greater, respectively, when combined with the new power MOSFET–diode–based limiter versus the resistor–diode–based limiter. Therefore, these results demonstrate that the power MOSFET–diode–based limiter is capable of producing lower signal attenuation than the three conventional limiter designs at higher frequency operation.