A large dynamic range voltage controlled attenuator with improved linearity‐in‐dB for ultrasound applications

Abstract

SummaryA large dynamic range (DR) and high linearity‐in‐dB voltage controlled attenuator (VCAT) for ultrasound applications was presented. Continuous tunable VCAT implemented with Metal‐Oxide‐Semiconductor (MOS) transistors used as shunt devices was proposed in this work, and the linearity‐in‐dB performance was analyzed in detail. Nonlinearity of the shunt transistors operated in different regions resulted in poor linearity‐in‐dB attenuation of the VCAT, which was undesirable in an ultrasonic receiver system. An effective linearity‐in‐dB improvement scheme was then proposed. The full scale range of the input control voltage was divided into N intervals with a same equal‐length by uniformly distributed voltage values. At these division voltages, the attenuation gains were corrected to be the ideal ones by the tracing and comparing circuits. In this way, the non‐linearity‐in‐dB was limited to the intervals between the two adjacent corrected attenuation gains, and the overall linearity of the VCAT was improved greatly. Measurement results showed that the dynamic range of the proposed attenuator was 36‐dB, and the gain errors were in a range from −1.22 to −0.55 dB. The noise figures (NF) at the commonly used ultrasonic frequencies was below 6‐dB, and the S11 was better than −10 dB over the input range of the control voltage.