For this blog we have guest blogger (I am happy to say he is about to become a regular blogger) Piyush Sevalia, Executive Vice President, Marketing for SiTime.
It might seem counterintuitive that an active device solution consumes less power than a passive device. Every design engineer knows that a passive crystal resonator (XTAL) doesn’t draw power, so why use an oscillator in place of an XTAL in a power sensitive application? The answer becomes clear when total system power is considered.
Battery powered products typically employ one or more timing components. If a XTAL is used, it doesn’t draw current directly from the battery. However, to make the resonator oscillate, it must be driven by an oscillator circuit that resides on a MCU or SoC. And this on-chip oscillator circuit can burn a lot of power.
MEMS-based μ Power oscillators provide a lower power alternative to quartz crystal resonators. A highly optimized low-power frequency synthesizer and analog circuitry drives the TempFlat MEMSTM resonator to achieve factory programmable frequencies with microamp-level core currents. In power sensitive applications, a MHz resonator can be replaced with these μ Power oscillators and the on-chip oscillator circuit on the MCU/SoC can be turned off. As shown in the diagram below, a SiT8021 μ Power oscillator connects directly to the XIN pin and simply bypasses the on-chip XTAL OSC circuit, resulting in a net power saving at the system level.
When a μ Power oscillator replaces a crystal XTAL, the combined current consumption of the oscillator + MCU is lowered by 7% during the active state. Whereas in standby mode, 18% savings can be realized. During standby, the oscillator consumes only ≤ 0.9 μ A because all internal circuits are turned off with the exception of the MEMS oscillator circuit and the ST pin detection logic.
In addition to consuming less system power, SiTime’s μ Power oscillators – measuring only 1.5 x 0.8 mm – consume less board space, an important factor since many power sensitive products are also space sensitive.
Another advantage of using an oscillator is its capability to drive multiple loads – something XTALs can’t do. When driving more than one load, power consumption increases only fractionally, compounding the power savings benefits of turning off OSC circuits onboard multiple chips (e.g., MCU + audio DAC). In addition to lowering system power, this approach reduces board space, BOM and costs.
When a MEMS-based μ Power oscillator replaces a quartz oscillator, the power savings are even more dramatic. In a portable audio application for example, a SiT8021 oscillator operating at 3.072 MHz draws only 60 μ A compared to a quartz oscillator at 2.5 mA. In this case, the power consumption is 98% lower. This can effectively extend battery life by a full day – a huge improvement.
SiTime’s revolutionary MEMS and analog technology delivers a solution that lowers total power consumption dramatically. If low power is critical, look at the big picture for big system-level improvements.
Related blog : Shattering the Limits of Power, Size and Weight