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| Advancement in Phase Locked Dielectric Resonator Oscillators |
By:
Mark |
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Phase Locked Dielectric Resonator Oscillators (PDROs) are widely used in both commercial and military applications. PDROs offer low cost, small size, low noise, efficient power consumption and high reliability required for local oscillator generation in commercial applications such as modern radar, communication, and test instrumentation systems. PDROs offers lower phase noise, lower spurious, smaller size, millimeter wave frequencies of operation, and higher output power options.
The standard PDRO consists of a BJT or GaAs MESFET fundamental Voltage Tuned Dielectric Resonator Oscillator (VTDRO) which is phase locked via a sampling loop to a low noise crystal oscillator reference. The phase locked loop (PLL) acts as a low pass filter to the multiplied up reference phase noise and as a high pass filter to the VTDRO’s phase noise.
In order to take advantage of these low noise references, the PLL noise floor of the PDRO needs to be equally low. If the noise floor of the PLL is not low enough, the noise floor of the PLL will limit the noise inside the loop. Digital loops with 100 MHz phase detector frequencies have a limited noise floor of around -150 dBc/Hz. In contrast, the sampling phase locked loop in the PDRO exhibits a typical phase noise floor of -162 dBc/Hz with a 100 MHz phase detector frequency. Equally important to the performance of a sampling PLL is the design of the reference amplifier. The reference amplifier on the input of the PLL must not degrade the reference phase noise. This amplifier must also maintain a constant signal level to the phase detector over variations in temperature from -45 to +85ºC along with reference level variations of +/- 5dB.
Through the use of proprietary sampling phase locked loop circuitry, single loop PDRO models provide exceptionally low phase noise, typically -120 dBc at 10 kHz offset from a 13 GHz carrier when phase locked to an external 100 MHz crystal reference. This proprietary low loop phase noise floor, along with the inherent low phase noise of the VTDRO, allows the use of wide loop bandwidths of approximately 200kHz to 300kHz. Wide loop bandwidths enable low microphonics and phase hit free operation, two critical parameters in both commercial and military systems.
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