8 - Intentional circuit compression

Summary

Designing circuits for intentional compressed operation is a much rarer task than designing for conventional linear amplifiers. It is no surprise that many of the tools and techniques developed for linear circuit design do not apply to these compressed designs. This chapter goes into the important design details for operation well into the transistor compressed operating regimes. More importantly, details on what is required to actually get to a switching RF power stage are worked out. The design procedures also point out if such a design with the available transistor technology is physically impossible.

Since linear (L-mode) operation, defined in Chapter 4, requires operating within the CCS region of transistor operation, here we de fi ne nonlinear operation as any other mode of operation. This means that both C-mode and P-mode are nonlinear operating regimes. From the operating mode discussion of a 3-port amplifier in Section 4.1.6, C-mode operation is more apparently nonlinear than P-mode. Chapter 6 demonstrates how both of these modes are useful only to intentionally compressed transmitters, just as Chapter 5 showed that both of these nonlinear modes force ET transmitters to violate the fundamental tenets of ET.

Device characteristic curves for both C-mode and P-mode are in the transistor resistive region, away from its CCS region. All locations in the resistive region of the characteristic curves are closer to the I-axis than any part of the CCS region, meaning that transistor power dissipation is always lower in the resistive region than anywhere in the CCS region. This also holds for transistor cut-off (no current) operation, which is a nonlinear operation at the voltage axis, where instantaneous power dissipation is zero. Lower power dissipation corresponds directly to higher energy efficiency. Therefore, nonlinear transistor operation provides better energy efficiency than any linear (meaning continuous current) transistor operation.