Chapter 8 presented superheterodyne radios of moderate current drain (e.g., >10 mA) that powered loudspeakers. This chapter will explore superheterodyne receivers with extremely low current draw that allow years of continuous playing on a single battery. What we will find out is that the superheterodyne circuit topology shown in Chapter 8 will not apply for low-power design, and instead, a modified circuit topology is required.
The design goals are as follows:
1. Current drain of less than 150 μA with a crystal earphone
2. Operational supply voltage of 1.2 volts
3. Sensitivity and selectivity performance at least equal to that of the four-transistor design in Chapter 8
As with ...