This paper presents a compensation structure to reduce the output common mode current of a rail-to-rail constant gm transconductance stage. The transconductance stage is a differential structure with the input transistors biased in weak inversion. This results in low power consumption and a simple relation between gm and tail currents. The constant gm is achieved by doubling the tail current in the active differential couple when the other one goes to cut off. Together with constant bias current in the output stage this can result in common mode bias current flowing from the output depending on the common mode input voltage. The proposed solution eliminates this problem by variation of the bias current in the output stage in relation to the tail currents in the differential couples. The transconductance stage was manufactured in a 0.35 um CMOS process. Measurement results are presented together with simulation data. The compensation structure cancels the common mode output currents for common mode input signals up to a frequency of 7 MHz.
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机译：本文提出一种补偿结构，以减少轨到轨恒定gm跨导级的输出共模电流。跨导级是一种差分结构，其输入晶体管偏置为弱反相。这导致了低功耗以及gm和尾电流之间的简单关系。当另一对有源差动耦合截止时，通过将有源差动耦合中的尾电流加倍来获得恒定的gm。再加上输出级中恒定的偏置电流，这会导致共模偏置电流从输出流出来，具体取决于共模输入电压。所提出的解决方案通过相对于差分耦合中的尾电流改变输出级中的偏置电流来消除该问题。跨导级是在0.35 um CMOS工艺中制造的。测量结果与仿真数据一起显示。补偿结构可消除高达7 MHz频率的共模输入信号的共模输出电流。
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