Abstract
This paper presents a calibration-free, 16-channel, 14-bit, 50-MS/s, pipelined successive approximation register (pipelined-SAR) analog-to-digital converter (ADC) for ultrasound imaging systems. A reference sharing scheme with reduced buffers is proposed to improve area-and-power efficiency, which is essential for multi-channel systems. Based on this, a three-stage, pipelined-SAR ADC architecture with reference/op-amp sharing and optimized stage resolution distribution is proposed. The prototype ADC is designed in a 0.18-μm process with peripheral circuits integrated, including low-voltage differential signaling (LVDS), bandgap, etc. It achieves a robust and calibration-free performance with 68.25-dB signal to noise and distortion ratio (SNDR) and 82.19-dB spurious-free dynamic range (SFDR), translating into a competitive figure of merit (FoM) of 0.47 pJ/conversion-step among other high-resolution ADCs used in ultrasound applications.
Highlights
After being reflected by the target to be measured, the echo signal is converted into an electrical signal by the transducer
The electrical signal is first amplified by the low noise amplifiers (LNA), by the programmable gain amplifiers (PGA) according to the attenuation during propagation
Bringing Equation (2) into (1), Equation (3) shows that the overall area is determined by the stage resolution distribution and the number of op-amps (Nop) and references (Nref)
Summary
Ultrasound imaging is widely used in non-destructive testing and medical examination because it is simple, cheap, and non-invasive [1–3]. With the development of phased array and synthetic aperture technology, the number of receiving (RX) and transmitting (TX) channels in ultrasound imaging systems is increasing to obtain a larger scan range and higher resolution [4,5]. The electrical signal is first amplified by the low noise amplifiers (LNA), by the programmable gain amplifiers (PGA) according to the attenuation during propagation. The ADC often becomes the bottleneck of the whole system [6] It determines the final signal-to-noise ratio (SNR) of the images and significantly affects the complexity of the entire circuit system. The trend of ADCs for high-end ultrasound imaging systems is to increase the number of channels while maintaining high resolution [7–9]. Thanks to the limited bandwidth of ultrasound signal, which is usually less than 10 MHz, the requirement for ADC sampling rate is eased. The pipelinedSAR architecture that achieves high area-and-power efficiency becomes an attractive option in such multi-channel, high-precision, medium-speed scenarios
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