CHAPTER 4

Gm-C integrators for low-power and low voltage applications. A gaussian polyphase filter for mobile transceivers in 0.35 m m CMOS.

---

4.1. Introduction

At low supply voltage, the key problem of analog signal processing functions is dynamic range reduction [1], [2]. This is especially severe in mixed mode systems due to the cross-talk produced by adjacent digital functions. For this reason, a key target is to keep the largest possible voltage swing. Bipolar based transconductors can be widely tuned with negligible variation in the V_BE voltage [3]. At low supply voltage, this does not impose restrictions on tunability of the transconductors. On the contrary, in CMOS transconductors, large tunability needed to correct for temperature and process variations gives a significant reduction in voltage swing at low supply voltages [3]. The new technologies are optimized towards digital applications and therefore, modern MOST’s, suffer from second order effects like velocity saturation and mobility reduction. New transconductor concepts which do not rely upon the ideal square law of a MOST, are needed. Another issue is to achieve large tunability without conflicting with the large swing requirement.