Design of a time-gain-compensation amplifier for ultrasonic echo signal processing

This article presents a design concept of a time-gain-compensation (TGC) amplifier integrated circuit (IC) for ultrasonic echo signal processing. The TGC chain contains pre-amplification, attenuation, filtering and comparison circuit blocks. An on-chip oscillator, bias circuit and digital control core are also included. The presented TGC IC concept blocks are designed and modeled using Cadence's IC design tools using a 250 nm CMOS process. The operational amplifier implemented in the TGC IC has a gain of 35 dB with a -3 dB bandwidth of 750 kHz, which corresponds to ultrasonic signal frequency range. The second order active band pass filter is of a Sallen-Key topology with a 274 MHz center frequency and a filter quality factor of Q = 1.018. A ring oscillator with external tuning capability is modeled at 448 kHz and has a 0.09 % frequency deviation. The ultrasonic echo processing chain has a digital output where the length of the pulse corresponds to the received signal strength. This makes the presented TGC IC concept suitable for both simple and complex ultrasonic, medical, industrial or research equipment.