test techniques
D-type flip-flop by a factor of 256 (or as high as 1024 for processes 0.25_m or smaller). The measured frequency (after the signal is divided) is typically on the order of 1-50MHz.
Given that the oscillation frequency is what’s being measured but the propagation delay is the actual parameter of interest, the next step is to calculate the propagation delay from the frequency measurement using this equation:
Figure 2.Ring oscillator signal spectrum through the S530 switch matrix
where: n is the number of inverter stages and fosc is the measured frequency of oscillation
Measurement considerations Parametric test systems have always been optimized to perform accurate, low-level DC measurements. However, AC performance for these systems is also important for supporting C-V measurement, pulse generation, and frequency analysis of ring oscillator structures.
The Model S530 Parametric Test System, for example, has been designed to provide high accuracy DC measurements over a broad dynamic range and with an AC signal bandwidth of 20- 30MHz. A frequency counter is often thought of as the best instrument for measuring frequency.
However, given that frequency counters count crossings (through zero, etc.), they can often produce erroneous readings in situations where the signal has to be extracted from a noisy AC environment. That’s why frequency measurements are often best performed using a spectrum analyzer or an oscilloscope using spectrum analysis techniques.
Spectrum analyzers operate by converting a signal from the time domain to the frequency domain using Fourier analysis. Each frequency in the signal’s spectrum is plotted versus its signal amplitude (Figure 2). That means, in a noisy signal environment, the signal of interest is often the one with the highest amplitude. Of course, in some instances, even spectrum analysis fails, such as when the amplitude of the signal of interest is below the noise floor of the system.
Frequency Measurement Software
Like many frequency measurement solutions, the S530’s frequency measurement option supports a variety of measurement commands:
ring_max ring_ref ring_Icc ring_meas freq_init freq_setup freq_measure Detects the frequency with the highest amplitude.
Detects the frequency that is closest to the specified reference frequency.
Detects the 5 frequencies whose amplitudes are larger than the specified threshold.
Determines the ring oscillator frequency and amplitude.
Initializes the oscilloscope card to its default state.
Sets the start frequency and end frequency of the scan as well as the resolution bandwidth.
Measures the frequency and amplitude of the strongest signal.
freq_measure_next Measures the frequency and amplitude of the next strongest signal as compared to the measurement returned by the freq_measure command.
freq_detect_peaks Returns the frequencies and amplitude of the specified number of peaks.
freq_selftest
Places the oscilloscope card in self-test mode and returns the status.
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