Power reduction techniques for CMOS current mode pipelined ADCs

The supply voltage of advanced CMOS technology is reduced to 1V or less. It is very difficult to design high performance analog circuit at this supply voltage because of the limited dynamic range. One possible solution is to use current mode circuit technique which is less sensitive to the limited dynamic range. Moreover, current mode circuit is more suitable for low voltage applications compare to the conventional voltage mode circuit. This research uses analog-to-digital converter (ADC) as a vehicle to investigate current mode design techniques with a main focus on power reduction.;The power reduction techniques are carried out in both circuit and system levels. At the circuit level, a new sub-stage design using voltage comparator is proposed to reduce power consumption without any performance degradation. At the system level, we observe that the signal-to-noise ratio (SNR) of a current mode pipelined ADC is proportional to the input current level, and the SNR of a pipelined ADC is dominated by the first few stages. Thus, it is possible to reduce the power consumption without significantly degrading the SNR by gradually reducing the current level of each stage along the pipeline. A 12-bit CMOS current mode pipelined ADC test chip is designed with a 0.35mum CMOS digital process. The measured signal-to-noise and distortion ratio (SNDR), spurious free dynamic range (SFDR) and total harmonic distortion (THD) are 64.90dB, 67.79dB and -67.02dB, respectively. The effective number of bit (ENOB) achieved is 10.49-bit and the calculated FOM is 1.31pJ, which has the lowest power consumption among reported current mode ADCs.;In addition, we can further reduce the power consumption by reducing the number of interconnects. We propose to use a quaternary (4-level) logic output to replace the binary (2-level) logic output, which will reduce the number of interconnect by half. A 6-bit current mode analog-to-quaternary converter (AQC) test chip is designed with special current mode quaternary logic functions.