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An arbitrary transfer characteristic (TC) amplifier, called the tanh cascode cell (TCC) amplifier, is reported. This novel amplifier is capable of synthesising an arbitrary TC including the ideal rectifier transfer characteristic, which is highly desirable for analogue circuits such as power amplifiers, low-noise amplifiers, mixers, op-amps, instrumentation amplifiers etc. The flexible transfer characteristic, wide dynamic range and high linearity capability of the TCC amplifier are demonstrated with a 16-cell MOSFET prototype.
Introduction: Over the past six decades electronic transistors have evolved from generation to generation [1]; however, the basic shape of their transfer characteristic (TC) remains similar to that shown in Fig. 1. It is well known that the minute details (including derivatives) of the TC shape of a transistor are of paramount importance to the linearity/ distortion of an amplifier. To date a few amplifier TC manipulation techniques are known to designers, such as the derivative superposition [2], the multi-tanh technique [3], and others [4-7]. The derivative superposition method [2, 4-6] is a single-ended topology but the dynamic range performance appears to be limited by the inherent nonlinearities of the devices. Multi-tanh techniques [3, 7] are based on differential pair topologies making them unattractive for power-efficient applications such as class A or B linear power amplifiers.
In this Letter, we introduce the tanh cascode amplifier, which is capable of achieving arbitrary TCs, including the ideal rectifier transfer characteristic (IRTC). The goal is to provide an analogue circuit synthesis technique that offers circuit designers more freedom to engineer various amplifiers TC to their needs. The Letter focuses conceptually on how to attain specific TCs with the tahn cascode cell (TCC) amplifier but not the specific applications that would benefit from such capability.
TCC amplifier: Fig. 2 shows the synthesis concepts of a TCC amplifier with 16 single-ended basis cells. Each basis cell is engineered to exhibit a tanh-like IV TC with turn-on and saturation features as shown in Fig. 2. With appropriate offset (shifting) and magnitude (scaling) arrangement, virtually any single-ended TC can be synthesised with a sufficient number of basis cells. For instance, in Fig. 2a practical...