Application ocxos 10mhz reference in GPS disciplined oscillator(GPSDO)

In the quartz crystal frequency, crystal resonator (XTAL), and oscillator (XO) is very wide, and long-term stability can be comparable to the atomic clock. However, 10mhz GPS disciplined oscillator(GPSDO) is not familiar to everyone. With the popularity of 5G and automatic driving applications, the use of GPS as a disciplined crystal oscillator (GPSDO) will be more and more, today we will introduce ocxos 10mhz reference application.

1. Working principle

GPSDO is currently one of the most trusted and accurate clock sources. The structure is generally composed of a highly stable crystal oscillator and a GPS receiver, and therefore also referred to as GPS disciplined crystal oscillator (GPSDO).

When working, GPSDO is the reference signal by the second pulse signal output by the GPS / BDS receiver, and the frequency offset of the compensation of the constant temperature crystal (OCXOS) is corrected by signal tracking loop.

The output signal is disciplined from 10-7 to 10 ^ -12 levels of the GPS device or GNSS satellite signal. GPSDO's working principle is similar to lock-phase rings (PLL), and some GPSDO is still using a PLL circuit, and most GPSDO has replaced PLL through the MCU to achieve compensation for frequency, temperature, and other environmental parameters. GPSDO's charm lies in the perfect combination of GPS signals with quartz crystals. 

Here, the GPS receiver provides excellent long-term stability, but its short-term stability is submerged by many factors: such as the internal resolution of the reference timing circuit, monolithic (1PPS), signal propagation effect (such as multipath interference), Atmospheric environment, etc. These are exactly the home court of existing high quality crystals (such as OCXOS), which is well known that OCXOS has better short-term stability, but exposed to heat, aging, and other long-term environments.

In this way, the GPS receiver and OCXOS integration in one GPSDO crystal is a high stability crystal device having good short-term stability and long-term stability, and its output signal can be accurate to the nanosecond (NS) level, frequency accuracy and long-term. The stability can reach the picosecond (10 ^ -12), which is useful for satellite navigation applications that require very precise time signals.

2. Performance parameters

By built-in GPS receiving module, the disciplined crystal oscillator (GPSDO) can be selected as a disciplined signal with GPS or 1PPS, and the accuracy and stability of the atomic clock level are reached by tame lock, and the phase error is controlled within NS (RMS). 

GPSDO has an absolute price and performance advantage over the traditional GPS-OCXOS reference scheme. GPSDO has a high cost performance than the atomic clock. These parameters include: 

(1) Time accuracy: generally nanoseconds.

(2)Disciplined phase accuracy: generally do tens of NS RMS. 

(3) Power consumption: generally areound 1W. 

(4) Disciplined input: Built-in GPS reception, you can also select external 1PPS input to tame. 

(5) Output: GPS NMEA, 10MHz CMOS, 1PPS CMOS.

(6) Shape, small size, and application more flexible.

To reduce costs, some manufacturers have begun to replace constant temperature crystal vibration (TCXO), which has achieved higher cost performance, and power consumption can be as low as 0.6W.

3. Typical application

With the large-scale popularity of 5G intelligent terminals, GPSDO application scenarios is increasing, such as timing and positioning in a variety of environments such as radar, satellites, and critical infrastructure, and reference clocks for testing measuring equipment.

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