Phase Noise of a Resonant-Tunneling Relaxation Oscillator

Experimental results are presented for the phase noise of a relaxation oscillator consisting of a resonant-tunneling diode in series connection with a transmission line, one end of which is shorted. Unlike constant-wave negative-resistance oscillators, the resonant-tunneling relaxation oscillator (RTRO) emits a sequence of sharp current pulses that are mode locked to the fundamental mode of the cavity formed by the short-circuited transmission line. The phase noise in the RTRO was investigated with and without injection locking by a weak sinusoidal source. Injection-locking gain of 51 dB was measured for fundamental injection locking. Subharmonic injection locking was demonstrated out to the 12th subharmonic. Also, timing jitter as low as 200 fs was measured for an RTRO that emitted ∼ 30 ps pulses at a repetition rate of 1.1 GHz.