Transient-imposed limitations of negative group delay circuits

In this paper the transients in gain compensated negative group delay (NGD) circuits are investigated. The study is conducted on an active unity gain NGD circuit with an RLC resonator integrated in the feedback loop of an operational amplifier. The circuit operates at a center frequency of 454MHz, and it is cascadable. The single stage circuit exhibits a NGD of 1.52ns and a gain of 0.69dB, with a fractional bandwidth of 23%. The circuit transient response to a step-modulated sinusoidal input is measured for a single-stage and two-stage circuits, showing a good agreement with analytical results. The analytical study is extended to general NGD multi-stage circuits based on RLC resonators and shows an exponential relationship between the transient level and the square of achieved NGD. We show that when considering information transfer applications, there is a limit on achievable NGD.