Sep 04, 2013

New MEMS Oscillators

posted by Bryon Moyer

Quartz is under attack yet again. While some folks are bringing quartz into non-timing applications, others are trying to squeeze it out of its primary application: timing.

Sand 9 is the latest such company, having just debuted their basic platform. They point to some fundamental limitations of quartz as a material, limitations we’ve lived with for a long time. Issues they highlight in particular are vulnerabilities due to vibration and shock, degradation at high temperatures and frequencies, issues with rapid temperature dips, inconsistencies between suppliers, and something called “activity dips.”

These latter sound really obscure – and yet Sand 9 say that they constitute the cause of 0.5% of all cell phone failures. The problem occurs when secondary vibration modes move around due to stresses and temperature – and they move in a way that’s different from the fundamental. So those modes may actually cross the fundamental, causing what Sand 9 refer to as a “heart attack.”

Their solution to this is a silicon-based one – and they had to deal with the problem that silicon on its own has much worse temperature performance than quartz does (3000 ppm vs. 20 ppm). That’s because silicon softens as temperature goes up. But, conveniently, SiO2 gets stiffer with higher temperature – so they have brought the two together in a sandwich to counteract each other, giving stability of less than 200 ppm.

So they have a six-layer stack: on top is the inter-digitated transducer, which acts as a top electrode and gets the whole thing oscillating. This overlays a layer of AlN, which sits atop the bottom electrode. Below those are relatively thick layers: a sandwich of oxide/silicon/oxide that provides temperature stability.

From a product standpoint, they’ve announced two families and hinted at an upcoming third.

  • The simplest one, the MR family, is just a resonator targeted primarily at Internet of Things devices communicating via Bluetooth Smart.
  • The second is the TSMR family. The “TS” stands for “temperature sensing”; it has a built-in heater and temperature sensor for use in the factory in calibrating and dialing up compensation. The target is cell phones.
  • Hinted at is a future TSMO (O for Oscillator) family that will have a silicon cap with an integrated oscillator circuit. Also targeted at cell phones.

All of them are provided in wafer-level chip-scale packaging (WLSCP) for integration into systems-in-package (SiP) assemblies. They claim no activity dips or susceptibility to vibration (> 10-10/G) or shock (30,000 G) and excellent phase noise performance.

You can find out more in their announcement.

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Aug 29, 2013

Stable Video, Easier Development

posted by Bryon Moyer

There are times when a shaky video can be just the thing. Imagine: where would the Blair Witch Project have been without it? What would an entire generation of hipsters do without the ability to shake (ironically) their video? How are happening new producers supposed to attract new audiences without being able to make their video look shoddy and unprofessional?

But, aside from those times, shaky video is not so good. In fact, for a lot of us, even these examples aren’t great (some of them representing videos that only their producers could love). We all have a hard enough time holding our cameras still without having to add shaking as part of some obscure production value.

We already take care of this for still pictures using optical image stabilization (OIS); why not simply apply that technology to videos? Well, for the same reason you don’t use a still photo camera to shoot video. Oops! Wait… I guess these days you can. OK, then simply because video isn’t the same as a still picture, so what works for one doesn’t necessarily work for the other.

First of all, still photos are just that: still. Any movement is wrong (except for things like sports, I suppose). So, in theory, you can just neutralize any motion, period. But, as you can imagine, that’s not going to work with video – unless you want to turn your video into a still shot. No, video means motion by definition. So when stabilizing a video image, you have to figure out what motion is intended and what motion is due to unwanted shaking.

Unlike OIS, which is typically implemented as hardware embedded into the camera module, CEVA is proposing handling digital video stabilization (DVS) in software for things like smartphones, wearable electronics, and cameras mounted inside moving vehicles, all of which involve inherent shaking. And all of which benefit from low power – wearable cameras in particular.

So CEVA has put together a set of DVS functions optimized to work on the CEVA-MM3101, their imaging-oriented DSP platform. These functions come with a number of options and parameters, since one solution doesn’t necessarily solve all the problems optimally. And with no standards out there, they see this as an opportunity for their customers to differentiate their camera solutions.

Other reasons for using a programmable solution instead of a hardware version are the fact that the DSP hardware can be reused for other functions – or can combine DVS with other functions like Super-Resolution.

Their solution provides correction along four axes: the x/y/z directions and then one angular direction: roll (which they call rotation about the Z axis, so I guess the convention is that forward is along the Z axis). They also provide correction for the “Jello effect”: this is distortion that occurs due to a shutter that’s rolling while the image or camera is moving, causing something of a relativistic leaning effect. And they can scale to handle 4K Ultra HD on a single core and adapt to various lighting conditions.

But power is also critical: they say that existing solutions use around 1 W of power; they’re touting less than 35 mW for 1080p30 video when implemented on a 28-nm process.

This new set of libraries could be integrated into an application using their new Application Development Kit (ADK), which they announced at the same time. The ADK is a framework for easing application development and optimization.

One noted feature is called SmartFrame. This allows a developer to operate on an entire video frame while the underlying framework takes care of logistical details. In particular, it can tile up the frame and apply “tunneling” to multiple algorithms, which they refer to as “kernels.”

This tunneling combines a pipeline architecture with the ability to chain multiple kernels together for back-to-back execution. Without tunneling, each kernel would be called by a program, and execution would return to the calling function after the kernel completed so that the program could then call the next kernel.

Instead, the framework allows the first kernel to work on one tile and then hand that tile directly off to the next kernel in the chain while the first kernel starts work on the second tile. And so forth for additional tiles and kernels. This minimizes the amount of data copying needed, and control doesn’t return to the calling program until the entire frame has been processed by all of the kernels.

The ADK also makes it possible to call DSP offloads from CPU programs, something we saw with CEVA’s AMF announcement.

You can find out more about CEVA’s DVS capabilities in their DVS announcement, and there’s more about their ADK in their ADK announcement.

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Aug 28, 2013

Two Ways to Tune an Antenna

posted by Bryon Moyer

We’ve looked at a couple of companies focusing on improving the performance of cell phone antennas in real time as conditions change. WiSpry (MEMS) and Peregrine (SOS CMOS) were two such examples. But Cavendish Kinetics came into the picture as well, and it turns out that there’s another layer of nuance as to what these companies do.

According to Cavendish, there are two ways to improve antenna performance: tune the impedance and tune the frequency. In the former case, you have an antenna that has to work with multiple frequencies, but is not specifically optimized for all of those frequencies. But as conditions or utilized bands change, the impedance matching may not be optimal. So companies like WiSpry and Peregrine provide capacitor networks that allow real-time tweaking of the impedance to reduce signal loss.

But Cavendish Kinetics claims to be doing something different: the capacitor arrays they create aren’t for adjusting the impedance; they’re for re-centering the frequency of the antenna. While they say that impedance tuning can improve the signal by 20% or so, they claim that they can get a 2X improvement in signal strength simply by tuning the antenna to whichever frequency is in use at a particular time.

We’ll look more at the specifics of how they create their capacitor arrays in a future story, but that’s secondary to the fact that they’re actually trying to solve a different problem than folks that, on the surface, would appear to be doing the same thing.

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