In addition to wristwatches, the need for GNSS is spreading to various IoT (Internet of Things)-related fields such as activity meters, child monitoring and drone tracking. If the power consumption can be drastically reduced without lowering sensitivity, the GNSS market can be considerably expanded.
Operational amplifier employed for DC feedback circuit
Sony has two basic strategies for the reduction of the reception chip's power consumption. First, the company reduced operating voltage to 0.7V. Second, it employed a 28nm FD-SOI (fully depleted silicon on insulator) transistor, whose operation efficiency is higher than that of conventional silicon (Si)-based transistors. The company announced those strategies in January 2015.
However, when operating voltage is lowered, operation becomes unstable, and sensitivity lowers. This time, Sony also announced two technologies to stabilize operation. First, it formed a DC feedback circuit using an operational amplifier in the low-noise amplifier (LNA). Second, the company added a positive feedback circuit using an operational transconductance amplifier (OTA) to the low-pass filter (LPF) used to extract baseband signals. Moreover, Sony added three resistive elements to reduce output impedance.