A Note on the Construction of Wideband Admittance Bridges

It is necessary to have precise control over the phase relation of the voltages on the unknown and the standards, in order to measure accurately, by bridge methods, the small component of an admittance composed of a small real part, and a large imaginary part, or vice versa. Under adverse conditions (i.e., when the argument of the admittance is within 1° of the axis), a phase error of only 0.1° can introduce an intolerable error. This problem is analyzed by standard methods, and after some reasonable assumptions are made, an explicit expression for the error is presented. Compensation is discussed, and a procedure for eliminating the largest part of the error is given. It is shown that the phase error of a simple phase inverting amplifier caused by a finite rise time is easy to compensate, while that due to delay is not so easy.