High-speed quantizer circuits, such as latching comparators, can be used to build sophisticated digital signal processing systems, including systems which digitize microwave signals. Comparators of this type convert analog signals into digital data under the action of a clock signal. Where the clock signal has a high frequency, for example from about 1 GHz up to 500 GHz or more, one known type of latching comparator has two resonant tunneling diodes (RTDs) which are coupled in series, and operate with very low power consumption. In one configuration of such a comparator, complementary versions of a single clock signal are supplied to respective ends of an arrangement that includes the two series-coupled RTDs. While this known approach has been generally adequate for its intended purposes, it has not been satisfactory in all respects.
More specifically, this approach provides good comparator sensitivity, frequency bandwidth and sampling rate, but only where the two RTDs are very closely matched in their electrical characteristics, and where there is very precise control of both the amplitude and phase of each of the complementary clock signals. A few degrees of phase mismatch in the clocks, or a few percent difference in RTD characteristics, can cause a loss in sensitivity of 10 dB, or significantly more.