Transceiver design for reciprocal operation of ultrasonic flow measurement systems

In transit-time ultrasonic flow measurement systems, the system's ability to operate reciprocally in the absence of flow is a highly desirable property. If the reciprocity is lacking in the system, any time delay that appears between the upstream and downstream signals at zero-flow conditions will result in false flow measurement. This phenomenon is known as the zero-flow error. This thesis presents a system in which the reciprocity property has been ensured by matching the electrical impedances of the front-end electronic circuits, namely: the output impedance of the transmitter Z$_\text{out}$ and the input impedance of the receiver Z$_\text{in}$. To achieve this, a circuit has been developed that can be used as both a transmitter and a receiver. This is the main feature that distinguishes the proposed design from those presented in previous work. The transmitter-receiver circuit has been implemented using a three-stage operational amplifier in unity gain feedback configuration. The class AB output stage of the amplifier is equipped with an additional function being used in receive mode for sensing and amplification of the signal. The simulation result obtained by the cross-correlation method yields a zero-flow error value of 30 fs, which is at least by three orders of magnitude smaller than the results achieved in prior work. The input and output impedances are equal to Z$_\text{in}$=73.2$\angle$80.7$^ \text {o}$ m$\Omega$ and Z$_\text{out}$=79.6$\angle$77.3$^ \text {o}$ m$\Omega$ respectively. A small mismatch remaining between the impedances prevents perfect reciprocity to be established in the system. A prototype IC has been taped out in TSMC 0.18 µm BCD Gen2 technology