Oscillators boast the best of both worlds

A new class of temperature-compensated oven-controlled crystal oscillators delivers the stability of an OCXO with the low power consumption, small size and light weight of a TCXO.

C-Mac Microtechnology has unveiled the world's first TC-OCXOs (temperature-compensated oven-controlled crystal oscillators), designed to deliver the high stability of an OCXO from a device with low power consumption, small size and light weight comparable to those of a TCXO.

Capable of stabilities better than +/-0.05ppm over operating temperature range, C-Mac TC-OCXOs will initially be aimed at mobile, battery powered and remote applications such as GPS, satellite comms, distress beacons and secure radio.

Ambient temperature variation is one of the main causes of frequency variation in a crystal oscillator.

To overcome this, C-Mac TC-OCXOs use a hybrid combination of limited temperature control, by use of an oven, and further reduction of the remaining frequency error through C-Mac's proprietary Pluto temperature compensation ASIC.

Previous attempts by various parties to combine temperature compensation with oven control have taken a crude "heating a TCXO" approach - a heater has been used to reduce the temperature range seen by the TCXO.

The result has been oscillators with good power consumption but significantly inferior stability to existing OCXOs.

C-Mac's TC-OCXO approach, for which patent protection has been applied, uses a miniature oven with crude temperature control to keep the crystal oscillator at an approximately constant temperature slightly above its specified operating temperature range - eg between 90 and 95C for a device with operating temperature range specified as -40 to +85C.

Any residual frequency errors occurring over the oven's limited temperature range are then minimised using the Pluto ASIC's analogue compensation circuitry.

The result is an oscillator with overall stability nearly an order of magnitude better than the most stable TCXOs - ie comparable to that of an OCXO - but with better power consumption, smaller and lighter package size and faster warm-up.

For example, a typical specification might offer +/-0.05ppm stability over a temperature range -20 to +70C, at standard frequencies from 5 to 20MHz, with a highly linear +/-5ppm frequency adjustment for ageing effects, power consumption around 400mW at -20C steady state or around 1.0mW during warm-up, from a 3.3V supply, in an industry standard 20.7 x 13.08mm DIL package.

Karl Ward, Senior Design Engineer with C-Mac Microtechnology, commented: "The TC-OCXO concept is made possible by our Pluto chip, which has the flexible features required to provide digitally programmable analogue compensation suitable for this design concept".

"Over the coming months, we will be introducing a range of compact, low-power TC-OCXO products offering OCXO-level stability for an increasing variety of applications".

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