Binary and Decimal Sample Rates

Synergy allows user selectable sample rates and sweep lengths which can be optimized for any application.

In a typical oscilloscope implementation, data is shown in a convenient decimal time per division such as 1, 2 or 5 ms enabling frequency and timing investigation at a glance. Since a scope display has ten divisions, this is easily accomplished if the sample rate is a decimal number (e.g. 1 MS/s) and the sweep length is also decimal (e.g. 10,000.)

Fig. 1: Oscilloscope-style display at 1 msec/div.

However, the requirements change when performing spectral measurements. The Fast Fourier Transform (FFT) is almost universally used for digital spectrum analysis because it is computationally efficient and well-understood. The algorithm relies on symmetries which require a binary number of samples, typically in the range of 1024 to 65,536 samples (although Synergy allows much longer sweeps if desired.)

Slightly less obvious is that the most convenient sample rates for an FFT are also binary. As is well-known, a 1024-point FFT produces 512 frequency bins between zero and the Nyquist frequency, one-half the sample rate. If a typical oscilloscope sample rate of 1 MS/s is used, each frequency bin is 976.5625 Hz wide. Cursor readout will indicate 1.953 kHz, 2.929 kHz, 3.906 kHz, etc. as in Figure 2 below. This is what you will find in FFT implementations for most DSOs. While correct mathematically, the scaling numbers are hardly convenient for quick comprehension.

Fig. 2: FFT Frequency Bins at 1 MS/s

A simple adjustment to the sample rate will improve the situation. If the rate is made 1.024 MS/s rather than 1.000 M, each spectrum line will become exactly 1000 Hz. The cursors will now read a much more friendly 2 kHz, 3 kHz, 4 kHz etc. as in Figure 3.

Fig. 3: FFT Frequency Bins at 1.024 MS/s

Just more of the flexibility you would expect from Hi-Techniques.

Explore Synergy Features

Synergy Architecture	Synergy Ethernet Connectivity
Anti-Alias Filtering	Binary and Decimal Sampling
Clear VU - Display Compression	Universal Signal Conditioning
Analysis and Report Generation	Download Synergy Brochure

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