A High DC Gain Op-Amp for Sample and Hold Circuits

Being a core component of an analog-to-digital converter (ADC), the operational amplifier is expected to provide sufficient DC gain and bandwidth to make the output amplitude less than 1⁄2 Least Significant Bit (LSB) in a half clock cycle. However, due to the limitation of the operational amplifiers in DC gain and bandwidth, most ADC is limited to 10-Bit, 100 Million Samples per Second (MSPS) [1-3]. This paper designs a gain-boosted operational amplifier in a 0.18um CMOS technology with a 1.8V supply. It is shown that the proposed amplifier achieves 89.8dB gain and 2.63GHz unitygain frequency, greatly outperforming competing techniques. In addition, the proposed amplifier supports 12-Bit resolution. Compared to other amplifiers with similar architecture, this one has a lower cost. Keywords-operational amplifier, DC gain, unity-gain bandwidth, ADC, CMFB