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Ultrasound - AD600 ground problems???

I?m a Brazilian researcher designing an ultrasound range finder fo Biomedical Department. This is a picture from Orcad project schematic:

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I placed an AC generator (Vin) to simulate the ultrasound reflected wav with 1mV amplitude and 700kHz. This is the simulation:
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Gain = 41dB.

I?m designing an ultrasound receiver with AD600 (Analog Devices) t amplify the reflected wave with a preamp supplied by an OPA350. I?m reall confused with all those AD600 ground connections and I?m aware if I make mistake it will produce a lot of noise and it will interfere in m measures. The AD600 IC provides separated ground references for inpu (A1LO/A2LO) and output (A1CM/A2CM). Datasheet warns: ?It is important tha A1LO and A2LO be connected directly to the input ground. Significan impedance in these connections reduces the gain accuracy. A1CM and A2C should be connected to the load ground.? I?m using the same single transducer element for transmission an reception then transducer has to be connected with transmitter an receiver circuits. In my schematic, I labeled ground plane with number 1 These are my ground considerations: ? Label 1 - I attached all transmitter components and DC regulator connected to VPOS (pin 13) and VNEG (pin 12) in AD600 to ground plane. ? Label 2 - I presumed that I should connect the input grounds (A1LO ? pi

3 /A2LO ? pin 6) and gate input (GAT1 ? pin 4/ GAT2 ? pin 5). At the sam reference, I connected the voltage limiter made by 1n4937 diodes and th preamp ground connection. ? Label 3 - I connected the output ground pins (A1CM ? pin 15 / A2CM ? pi 10) with the load resistor as an output ground reference.

Where should I connect the transducer? There are 2 options: the groun plane with the transmitter components or with the AD600 input groun reference. Should I isolate AD600 ground reference from next stage (buffer + pea detector)? Is it safe connecting peak detector and AD ground output t ground plane?

I?m so sorry for my poor English. Thanks in advance,

Claudio Klein

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Klein
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You are making things over-complicated. You simply want to make sure that no noise induced currents (which includes digital circuits) appear in impedences in the signal circuit or in any voltage reference circuits. So be aware of the currents, and make your connections accordingly. Also beware capacitive coupling.

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CBFalconer

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