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Linear Array CWDP Doppler Estimator Predictive ADC


When performing tissue harmonic imaging or Doppler ultrasonography, the low-amplitude echoes to be detected appear in the presence of intensive clutter reflections. Therefore, it is indispensable to maintain a wide linear range of the LNA in order to minimize high order products and intermodulation between signal components of different amplitude.
Regarding LNA noise performance, it is widely accepted that active termination of the transducer cable achieves superior noise figure as compared with a conventional (shunt) scheme.
At present, active termination is provided by the input impedance of an LNA configured as an inverting operational amplifier. Accordingly, the impedance looking into the inverting input is reduced by a factor 1+G, where G is the open-loop gain. Typically, 5 < G < 10.
While active termination improves noise figure of an LNA, this technique requires lowering the G. Consequently, those amplifier errors associated with finite open-loop gain become increasingly elevated. 
Our patent-pending architecture solves the most contradictive problems in designing ultrasound LNAs: low noise and wide dynamic range. The invention discloses an LNA comprising a class AB CMOS transconductor and an I/V converter connected in series.  Inherently exhibiting low input impedance, the transconductor provides active termination of a transducer cable.
Graphs below depict simulation results on  the  LNA's  large-signal  linearity and  noise performance.  The simulations were conducted  assuming use of a 0.25 um CMOS technology.

Cable termination by matching transconductor impedance
Transconductor linearity vs. matching impedance (RS = 50 Ohm)

Harmonic distortion of a single-tone 1 VP-P signal (R = 200 Ohm, RS = 1/gM = 50 Ohm)

Input-referred LNA noise (R = 1K, 1/gM = 50 Ohm, RS = 0)

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