A 64-Channel Transmit Beamformer With ±30-V Bipolar High-Voltage Pulsers for Catheter-Based Ultrasound Probes

This article presents a fully integrated 64-channel programmable ultrasound transmit beamformer for catheter-based ultrasound probes, designed to interface with a capacitive micro-machined ultrasound transducer (CMUT) array. The chip is equipped with programmable high-voltage (HV) pulsers that can generate ±30-V return-to-zero (RZ) and non-RZ pulses. The pulsers employ a compact back-to-back isolating HV switch topology that employs HV floating-gate drivers with only one HV MOS transistor each. Further die-size reduction is achieved by using the RZ switches also as the transmit/receive (T/R) needed to pass received echo signals to low-voltage receive circuitry. On-chip digital logic clocked at 200 MHz allows the pulse timing to be programmed with a resolution of 5 ns, while supporting pulses of 1 cycle up to 63 cycles. The chip has been implemented in 0.18- $\mu \text{m}$ HV Bipolar-CMOS-DMOS (BCD) technology and occupies an area of 1.8 mm $\times16.5$ mm, suitable for integration into an 8-F catheter. Each pulser with embedded T/R switch and digital logic occupies only 0.167 mm ² . The pulser successfully drives an 18-pF transducer capacitance at pulse frequencies up to 9 MHz. The T/R switch has a measured ON-resistance of $\sim 180~\Omega $ . The acoustic results obtained in combination with a 7.5-MHz 64-element CMUT array demonstrate the ability to generate steered and focused acoustic beams.