This article introduces the application of analog switches in cell phones. It describes the development history of analog switches since the 1960s, and focuses on ON Semiconductor's MC74VHC1G66DFT2 product, which is a low voltage, single switch (SPST) analog switch with a small size and features low resistance and high impedance.
This document is an application note from ON Semiconductor that demonstrates the utility of analog switches in cell phone designs. It addresses specific engineering challenges such as designing oscillators with multiple frequencies, reducing power consumption in Phase-Locked Loop (PLL) systems, and improving PLL lock times by adjusting time constants.
| Voltage Rating (MC14066) | 3.0 to 18 V |
|---|---|
| On-Resistance (MC14066) | ~500 Q |
| On-Resistance (MC74VHC1G66DFT2) | <25 Q |
| Delay (MC74VHC1G66DFT2) | <1.0 nsec |
| Distortion (MC74VHC1G66DFT2) | <0.1% |
| -3.0 dB Point (MC74VHC1G66DFT2) | >100 MHz |
To switch in a different crystal to have a single input to a device, such as slowing a microprocessor or DSP down to conserve power.
By using a sample and hold output where the PLL charges a capacitor and holds the charge for a period of time before reclosing the loop.
By allowing the designer to change the resistor or capacitor that makes up the time constant for a PLL to get close to lock quickly then go to a long time constant.