Transconductor

This chapter shows the basic concept and improved design of a transconductor. The transconductor is one of the most important building blocks in analog and mix-mode circuits, including multipliers [9, 10], continuous-time G _m -C filters [11, 12], volt age controlled oscillators [13], and continuous-time sigma-delta modulators [14]. Its main idea is to convert the input voltage into the output current with a linear transformation factor. The active device is used for replacing passive devices ow ing to power and area consideration with the tradeoff of the non-ideal performance. The main non-ideal characteristics of the transconductor are the limited linear input range, limited output impedance, finite signal-to-noise ratio, and finite bandwidth. The linear performance is the most important issue in the transconductor design. Moreover, as the feature size of CMOS technology scales down with supply volt age, the dynamic range, bandwidth, and power consumption will be limited under specific linearity.