A phase Noise Analyzer (PNA) is used to measure the phase noise of the signal. Phase noise of an RF component like oscillator can define as the noise arising from the short term, rapid, random phase fluctuations caused by time domain instabilities of the device. This fluctuation is also called phase jitter and it courses the generation of the noise spectrum, spreading out on both sides of a signal.
In Radio communication systems, even though phase noise spreads out equally on both sides of the carrier, it will measure only for one side, hence phase noise is referred to as single side-band phase noise.
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In this Phase noise Analyzer article, we will cover,
Phase Noise Analyzer is used to measure the noise in the sidebands of the signal which is generated due to short term, rapid, random phase fluctuation in the signal i.e. phase jitter.
Noise Figure Analyzer is used to measure the internally generated noise level of the device under test (DUT). Noise measurement involves applying a known noise at the input of the DUT and measuring the noise power at the output of the DUT and then calculating the ratio of the noise power at the input and output, to get the noise figure of the DUT.
Both Phase noise of a signal and Jitter of the signal indicates the timing instability of a signal. Phase noise is the signal instability expressed in the frequency domain, and Jitter is the term expressed in the time domain.
Phase noise in a signal can be measured using a dedicated phase noise analyzer, which can measure the phase noise in the range of -140 dBc @ 1 Hz Offset, -170 dBc @ 10 kHz Offset. Phase noise analyzers use dedicated external or internal references to measure the low-level phase noise (residual and absolute) which is close-to-the-carrier.
An alternative to a PNA is the measurement of phase noise using a spectrum analyzer which will have phase noise measurement features. Phase noise of the device under test (DUT) can measure in a spectrum analyzer only if the noise level is greater than the noise level of the spectrum analyzer's local oscillator. Spectrum analyzer based measurement can read the phase-noise in the range of about -100 dBc at 1 Hz offset.
RF and Microwave Phase Noise Analyzers are basically available as a Bench-top stand-alone unit, or PXI based Rack-mountable unit.
Bench-top Phase Noise Analyzer are generally AC power operated and will have the internal display and front panel keypads for the phase noise measurements. It is ideal for the analysis in the lab environment of R&D, and manufacturing of RF and microwave components like oscillators. The bench-top unit will have internal heat dissipation and accurate measurement capabilities, however, measurement capabilities, like frequency range or the phase noise amplitude cannot be extended in future.
Rack-Mountable Phase Noise Analyzers are available with PXI based cards. It will have higher measurement features and will have the features to expand the measurement ranges like frequency coverage, Noise figure level etc. These units are mostly working on remote interface and monitoring.
Phase noise arising from the rapid, short term, random phase will cause the degradation of the spectral purity of the oscillator. This will affect the communication systems' performance and cause random rotations, amplitude variation of received signals, spectral regrowth, channel interference etc. In a system, phase noise will increase by +6 dB for every doubling of the signal frequency and decreases by -6 dB for every division of the signal frequency.
Phase noise causes the degraded performance of data transmissions: If the phase noise performance for any local oscillators is not good, it will lead to the reduction of the signal margin and result in increasing the bit error rates in the data transmission.
Phase Noise caused to adjacent channel interference: In a transmission system if the phase noise is not kept below certain limits, the signal phase noise will spread out both sides of the signal and it will fall into nearby channels and will be causing interference to other nearby channel users.
To overcome the above issues in the communication systems, it is ideal to identify the phase noise of the source using a Phase noise analyzer during the R&D and manufacturing stage itself. Identification of the phase noise at an early stage helps to reduce it by proper design.
While selecting a phase noise analysis, three prime elements need to consider is Frequency of operation, Phase noise amplitude in respective frequency offset and Measurement Bandwidth.
The input frequency of the phase noise analyzer indicates the range of frequency over which it can perform the measurement on the DUT. In the case of PXI based phase noise analyzers, it can be extended such as up to 1.8 GHz, 26.5 GHz, up to 140 GHz etc. Need to select as per the DUT operating range.
Phase Noise Amplitude of the PNA is expressed in dB relative to the carrier, denoted as dBc (decibels down from the carrier). Higher the Phase Noise Amplitude range, the better the measurement requirements. It should be a minimum of 10 dB more than the expected maximum phase noise of the DUT.
The level of Phase Noise Amplitude measurement for each offset from the carrier needs to verify on the base of the expected phase noise offset of the DUT.
Example -140 dBc @ 1 kHz, 10 kHz, etc.
The noise power of the signal is proportional to its bandwidth. Typically measurement bandwidth of Phase Noise Analyzer is taken as 1 Hz bandwidth.
Accuracy of the PNA is referred to as the correctness of the measurements with respect to the reading obtained. Example 1 Hz – 1 MHz : +/- 2 dB. Higher accuracy over the entire operating range of the DUT is better for the application.
RF Connectors, external reference oscillators connectors and other electrical connectors used in the phase noise analyzer need to check to match the DUT connectors.
Phase noise of a signal is the representation of fluctuations in the phase of a waveform in the frequency domain. For example, digital communication-system engineers are concerned with the jitter of a clock signal, whereas radio-frequency engineers are concerned with the phase noise of an oscillator used in the system. A phase Noise analyzer is an ideal instrument used to identify the phase noise of the DUT and helps to correct it during the design stage.
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