Ring Oscillator VCO

Block Ring Oscillator VCO generates phase noise using a Gaussian noise source and a flicker filter.

When phase noise is included, the phase noise is calculated based on the variance of the stochastic period displacement process relative to the spectral density at one frequency. At the specified oscillation frequency , the frequency of the offset and single-band spectral density the variance of the period offset is

Thus, with the exception of flicker noise, the period offset obtained from an uncorrelated random process with constant variance is necessary. This period offset is generated by the Gaussian block noise source.

To simulate flicker noise, the flicker filter introduces an additional gain at low frequencies, up to four orders of magnitude lower than the conjugate frequency of flicker noise. To increase the spectral energy density with before the flicker filter should introduce a voltage gain below the conjugate frequency, while maintaining a unit gain above the conjugate frequency. To achieve this goal, the flicker filter is a recursive digital filter with an alternating sequence of four poles and four zeros. The lowest zero of the frequency is a constant factor higher than the lowest pole of the frequency, the next pole of the higher frequency is the same constant factor higher than the lowest zero of the frequency, and this pattern of alternating poles and zeros persists until the end of the sequence. The constant coefficient is a function of the exponent of the flicker filter, and for the nominal case of flicker noise The coefficient is equal to the square root of ten.

To minimize numerical noise in the flicker filter, the sampling frequency of the Gaussian noise source and the flicker filter is limited. 20-a multiple of the maximum phase noise offset frequency specified in the technical description, unless this sampling frequency is comparable or exceeds twice the oscillation frequency. For noise displacement frequencies with a higher phase response, the sampling frequency is limited to twice the oscillation frequency.

The variance of the Gaussian noise source is adjusted to compensate for the difference in the sampling frequency of the noise source and the oscillation frequency of the oscillator.

When the phase noise is turned off, the Gaussian noise variance is reset to zero.

These phase noise spectra often contain measurement artifacts that should not be included in the GONG model itself. Although the estimates of the phase noise parameters are They are often close to creating an adequate physical model. In some cases, a user assessment of the situation is required. Two common problems are the minimum noise level and the resolution band.

Sometimes the measured phase noise corresponds to the physical model up to the frequencies for which the phase noise may be lower than the minimum noise level of the measurement.

Apparently, the minimum noise level during measurement for a set of technical data is -140 dBn/Hz, and the phase noise of the device under test is probably below this minimum level at higher offset frequencies. 100 MHz. In this case, a set of parameter values that best match the data at lower frequency offsets is likely to produce a more accurate model.

Sometimes the measured phase noise corresponds to the physical model at all levels, except for the lowest frequency offset.

The most likely reason for this result is that the resolution band used for the measurement was too wide to obtain accurate results at the lowest frequency offset, in this case 30 kHz. Even if the carrier was outside the bandwidth of the measuring filter, the carrier energy that passed through the limited delay band of the measuring filter was significantly greater than the energy in the bandwidth. In this case, a set of parameter values that best match the data at higher frequency offsets is likely to produce a more accurate model.