Capacitive Charge-Based Transmitter

In light of all the potential noise and efficiency benefits discussed in Chap. 2, the first proof-of-concept charge-based transmitter implementation [Par15b, Par15a] is presented in this chapter. As it will be noted in the following paragraphs, this first implementation closely resembles the proposed watermill analogy, where the amount of power transferred to an output load is controlled by either increasing or decreasing the water level in a reservoir. Instead of buckets and valves however, switches and capacitors are used in this case to deliver controllable amounts of charge to a baseband capacitor. The motivations for choosing this first topology are manifold: First, an architecture exclusively based on switches and capacitors is inherently “digital friendly”, in the sense that it can be easily scaled and ported to different technologies following the typically dominant digital circuitry. Second, switches and capacitors are perhaps the only two components that benefit from scaling in advanced digital-oriented CMOS technologies. By making smaller transistors the intrinsic capacitances are reduced, allowing faster switching with less power consumption [Raz12]. The feature size reduction also provides larger capacitance densities, improving area efficiency with metal-oxide-metal (MOM) integrated capacitors. Third, and not less important, as further discussed in Sect. 3.2.3.2 the given topology also provides quantization noise scaling capabilities, relaxing the out-of-band noise emission. This chapter is divided into other four sections. Section 3.2 provides the architecture description with operating principles, followed by circuit implementation (Sect. 3.3) and layout considerations. Measurement results and conclusions are given in Sects. 3.4 and 3.5 respectively.