A Continuous-Time Pulse Compressor with Linear Frequency-Dependent Delay Achieving 1.66-µs Maximum Delay and Received Echo Enhancement by 6.7-dB for Ultrasound Imaging

This paper presents a continuous-time pulse compressor (CTPC) for ultrasound imaging systems with enhanced signal intensity and axial resolution. Conventional pulse compression using a chirp signal employs matched filtering, which performs cross-correlation calculations in the digital domain. However, the calculation requires a large amount of computing resources. The proposed CTPC performs pulse compression directly in the analog domain by frequency-dependent delay. In the proposed CTPC, a second-order all-pass filter (APF) with a relatively high quality factor (Q) of 1.8 achieves a long group delay (GD) to reach a sufficiently long chirp period in the ultrasonic band. Furthermore, cascading other second-order APFs with different resonance frequencies approximately linearizes the total GD with respect to frequency. We investigated the implementation of the proposed CTPC using discrete operational amplifiers and passive components. Measurements confirmed a 6.7 dB signal enhancement from compression effects with an ideal electrical chirp signal. Further acoustic measurements using an 8 × 8 channel 2-D matrix array probe and an imaging prototype demonstrated improved signal enhancement and compression factor of 3.2.