A Rail-to-Rail Transconductance Amplifier Based on Current Generator Circuits

In this brief, two current generator circuits are used to design a self-biasing transconductance amplifier. The current generators are configured using two n-channel and p-channel cascode current mirrors by which a high input dynamic range is achieved. Since such a topology creates positive feedback, the transconductance of the circuit is also increased causing higher performance. To ensure the stability of the circuit, constant current sources can be paralleled with the current mirror topologies, which of course are implemented using input drivers. Therefore, two n-channel and p-channel input differential pairs are added to the current generator circuits by which not only a rail-to-rail operation is achieved but also the amplifier is stabilized. The proposed circuit was fabricated in the TSMC 0.18- $\mu \text{m}$ CMOS process with a silicon area of $54.1\times 71\,\,\mu \text{m}$ . Under a 1.8-V supply voltage, the experimental results showed a high input common-mode range (ICMR), while a gain bandwidth (GBW) of 83.9 MHz was measured for a capacitive load of $2\times6$ pF. In addition, a dc gain and a slew rate (SR) of 68.4 dB and 71.7 V/ $\mu \text{s}$ , respectively, were achieved.