High speed photo-electronic analog to digital convertion using a laser strobed photocathode

High-speed applications such as satellite communications, high speed Ethernet, medical sensing and imaging, software radio, electronic instrumentation and signal cryptography require analog to digital converters (ADCs) with high bandwidth and bit precision. In most cases, the converter bandwidth defines the total system capability, which makes the ADC a critical component in these devices. The ADC bandwidth is fundamentally limited by the clock jitter that produces the sampling pulse train. Typical ADCs have clock jitter times of 0.5ps or higher. Furthermore, the resolution of electronic ADCs is limited by inherent quantization noise, thermal noise and comparator ambiguity. To improve clock jitter, mode-locked laser pulses have been proposed as sampling pulses at rates up to 150 GHz. Optoelectronic ADC's that combine modelocked laser technology with photoconductive sampling have reportedly demonstrated 4-bit resolution at 40 Giga-Samples per second (GS/s).; We have proposed an implementation employing a mode-locked laser to generate a low-jitter train of very short light pulses that illuminates a semiconductor photocathode at front end of a miniaturized vacuum tube. The emitted electron pulses are accelerated and deflected by the analog voltage applied between a pair of deflector plates. Each electron pulse samples the analog deflecting voltage that is then quantized according to the position of the detector receiving the pulse on the back end of the tube. We call this system LAVAMAC (Laser-strobed Vacuum-Microelectronic Analog to digital Converter).; Computer modeling of a 100nm thick semiconductor photocathode suggests that sub-picosecond electron pulses should be possible. Analysis of the electron optics of the tube indicates that 6 bit resolution at 100GS/s should be achievable.; To verify the above, a demountable streak camera with interchangeable photocathodes was designed and built. Using this experimental apparatus we have performed the first measurements of time response and photoemission jitter at 100GHz rate of 100nm thick InGaN photocathodes. The experimental results indicate that a 5 bit, 100GS/s quantizer is achievable with the InGaN photocathode.; Improvements of the basic ADC design include error correction, time multiplexing and single electron emitters.