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RTCs cut power use of design components tenfold

24 Mar 2015  | Bernard Cole

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In this product analysis, Bernard Cole detailed the importance of the lowly real-time clock among embedded developers. Particularly, he discussed how Ambiq RTCs can shrink the power consumption of the rest of the components in a design.

A basic hardware building block in any embedded developer's repertoire of low power design aids is the lowly real-time clock (RTC). In its simplest form, the function of an RTC is to keep track of the current time. But the RTC has taken on a pivotal role as the means by which to monitor and manage sparse power resources in almost any untethered embedded or Internet of Things (IoT) design.

So it should come as no surprise that almost every maker of microprocessors and microcontrollers also provides at least one RTC circuit in its catalogue of products, including most of the major makers of ARM-based processors and SoCs, including NXP Semiconductor, Silicon Labs and ST Microelectronics. The reason is simple: developers still have to deal with the power requirements of the rest of the components in a design.

Ambiq Micro has addressed this challenge by using the Subthreshold Power Optimized Technology (SPOT) used in its Apollo family of ARM Cortex-M4F MCUs to also fabricate its AM08XX/18XX real time clock family (Figure 1), now in volume production.

Subthreshold voltage CMOS process

Figure 1: Using a subthreshold voltage CMOS process, Ambiq Real-Time Clocks lower power of all devices in an embedded design.

In an interview with EE Times, Ambiq Vice President of Marketing Mike Salas said as a result of the incorporation of SPOT, developers using Ambiq RTCs can reduce the power consumption of any component in a design tenfold, including the MCU/MPU. He said the company's tests indicate that using one of its subthreshold voltage-based RTCs in a system will reduce current—and thus power consumption—to no more than 55nA with an external crystal, 15nA with a standard resistor–capacitor circuit (RC circuit) or 21nA using an auto-calibrated RC.

"The RTCs we have built allow the design of systems that are roughly seven times lower in power than the NXP PCS 2123 RTC, and at least 10 times lower than similar devices from Integrated Device Technology, Maxim, and STMicroelectronics," he said.

Ambiq RTCs

Figure 2: Due to the use of its subthreshold voltage process, Ambiq's family of Real-Time Clock circuits outstrip the capabilities of most competitors.

And because they are processor agnostic, Ambiq's RTCs can reduce the power consumption of any embedded system design based on any processor, including high end ARM, MIPS and Intel Atom-based 32- or 64bit CPUs as well as any 8- or 16bit microcontroller.

If these claims are proven in working designs, the near-term impact of Ambiq's RTC family is more far-reaching than the use of its subthreshold voltage technology in 32bit processor designs.

The shift to threshold voltage-based RTCs will make any 32bit MCU more viable in power constrained IoT designs. But at the same time, it will make already low power 8- and 16bit MCUs even more so, considerably extending their operational life, especially in applications that require unattended operation over months or years using only batteries or energy harvesting. The AM08XX/18XX devices achieve this power savings in a number of ways, Salas said.


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