An ultrahigh-speed continuous-time delta-sigma modulator using a 4-level resonant-tunneling quantizer has been investigated. The quantizer consists of four resonant-tunneling diodes (RTDs) and a source-coupled high-electron-mobility transistor (HEMT) pair, and operates in the fully-differential mode. Circuit simulation shows that the present first-order delta-sigma modulator has a signal-to-noise ratio (SNR) of 49.4 dB at a sampling frequency of 10 GHz and an input bandwidth of 100 MHz. An improvement in the SNR by 5.6 dB is obtained by increasing the number of quantization level from two to four.
['Keisuke Eguchi', 'Masaru Chibashi', 'Takao Waho']
A design of 10-GHz delta-sigma modulator using a 4-level differential resonant-tunneling quantizer