# Phase noise testing

## “ Optimizing PLLs ”

The solution to phase noise measurement and testing of oscillators is the Agilent E5501B opt 201 phase noise measurement system. With excellent noise performance from the HP 8665B signal source, results from the system out perform other phase noise measurement techniques.

### Agilent E5501B phase noise measurement system

The system can perform measurements, testing and analysis of the phase noise of one port devices, including:

- PLL frequency synthesizers.
- VCOs and other oscillators.
- TCXOs and other types of crystal oscillator.
- DROs.

The system also measures:

- Baseband noise sources, such as power supply noise.
- Residual noise of two port devices.

Phase noise measurement systems are performance limited by the reference source used to make the measurement. The HP 8665B Opt.004 reference source has one of the lowest phase noise profiles on the market.

When using the HP8665 the system can measure devices up to 6 GHz at offset frequencies up to 100 MHz. Electronic storage of results allows easy comparisons to be made between measurements.

Phase noise measurement system E5501B 360kb

Signal generator HP8665B 1.7Mb

The E5501 is one of the E5500 series of phase noise measurement systems from Agilent (including the E5502, E5503, E5504 and the E5505A).

### Phase noise profile

Phase noise profile

figure (1)

The system measures the phase noise profile or single sideband power due to phase fluctuations L(f). Results are displayed in dBc/Hz vs offset frequency in Hz.

In figure (1) a typical measurement of a phase locked loop can be seen, including the three main sources of noise. From left to right: slope of the reference noise, phase detector noise plateau, slope of VCO noise.

This type of plot shows noise levels exceeding the capabilities of spectrum analysers. It allows the designer to spot any deviation from the expected phase noise profile or any unexpected spurious signals from the device under test.

From the single sideband phase noise results, the system is capable of calculating the total integrated phase noise of the signal source, a method of expressing the quality of the signal source. Integrated results may be displayed in a number of formats.

#### Equations

L(f) df

Integrated single sideband phase noise. (dBc)

Sphi(f) = (180/π).

2.

L(f) df

Spectral density of phase modulation, also known as

RMS phase error. (degrees)

Snu(f) =

2.

L(f).f² df

Spectral density of frequency fluctuations, also known as

RMS frequency error or residual

FM. (Hz)

Sy(f) = Snu(f)/fosc

Spectral density of fractional frequency fluctuations.

### EVM and jitter

From these integrated results, it is possible calculate

RMS jitter and to approximate the

EVM contribution due to the phase noise.

Jitter = Sphi(f)/(fosc.360°)

Jitter due to phase noise. Note Sphi(f) in degrees.

Error vector magnitude due to phase noise. Note Sphi(f) in degrees.

It should be noted that the EVM equation shown above, is an approximation to the EVM contribution from phase noise. EVM is also degraded by a number of other system parameters such as filtering and non-linearities. The jitter equation is also only the jitter due to phase noise. Jitter can also be affected by effects such as cross-talk and mismatch.

To find out more about specific equipment or to discuss your particular requirement, please

contact Telestrian.