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Purnendu Bhattaru
(From: IIEST, Shibpur; To: Texas Instruments, Bangalore)
Conference Publications
- P. Bhattaru and N. Krishnapura, "A 36dB Gain Range, 0.5dB Gain Step Variable Gain Amplifier with 10 to 25MHz Bandwidth Third-Order Filter for Portable Ultrasound Systems," 33rd International Conference on VLSI Design, Bangalore, India, 2020.
Thesis
Title: Design of Low Power Analog Front-end for a Ultrasound Image Path Receiver
This work focusses on the design of a 32-channel fully-integrated ultrasound image-path receiver analog front-end (AFE), mainly intended for portable and mobile applications. Main objective of the aforementioned design is to integrate more number of channels than other available alternatives with a lower power dissipation per channel and without compromising much of the signal processing performance. The analog front-end is targeted to be designed within a static power budget of 8.5 mW/channel, input referred noise of 2.5 (spot noise spectral density at 5MHz), linear input range of 0.35 Vp−p, 0.5 Vp−p, 0.7 Vp−p (single-ended) and full-scale output of 2Vp−p (differential). The front-end comprises of three major blocks, namely, a low noise amplifier (LNA), a variable gain amplifier (VGA) and an anti-alias filter (AAF) preceding the ADC. In this work, the design of the VGA, AAF and dc offset correction loop of the LNA will be discussed.
LNA amplifies the single ended input to the front-end to a fully-differential output above the noise floor of succeeding blocks. The variable gain amplifier maps the LNA output to the input dynamic range of the ADC. It provides attenuation ranging from 0dB to −36dB with a resolution of 0.125dB (i.e., 288 steps) depending on LNA output signal amplitude. It also incorporates first-order filtering with a closed loop gain of 24dB and a programmable bandwidth of 10MHz, 15MHz, 20MHz, 25MHz. VGA has a full-scale input of 4Vp−p (differential), peak output swing of 2Vp−p (differential). This first-order filter is followed by a unity-gain second-order low-pass filter to realize a third-order Butterworth low-pass response required for anti-aliasing. The VGA and AAF, together consumes a total quiescent current of 1.55Ma at 270C from a supply voltage of 1.8V(nominal). Third harmonic distortion(HD3) is better than−60dBc for full-scale output(2Vp−p) at 5MHz. Output spot noise spectral density at 5MHz is less than 100.