How to Evaluate Oscilloscope Signal Integrity (.PDF Download)

Signal integrity is the primary measure of signal quality. Its importance increases with higher signal speed, oscilloscope bandwidth, the need to view small signals, or the need to see small changes on larger signals. Signal integrity impacts all oscilloscope measurements. Oscilloscopes themselves are subject to the signal-integrity challenges of distortion, noise, and loss.

Oscilloscopes with superior signal-integrity attributes offer better representations of your signals under test, while representations provided by those with poor signal-integrity attributes will be inferior. This difference impacts an engineer’s ability to gain insight and to understand, debug, and characterize designs.

Thus, selecting an oscilloscope that has good signal-integrity attributes is important; the alternative is increased risk in terms of development-cycle times, production quality, and the components chosen. To evaluate oscilloscope signal integrity, we will look at analog-to-digital converter (ADC) bits, vertical scaling, noise, frequency, phase response, effective number of bits (ENOB), and intrinsic jitter.

ADC Bits

Resolution is the smallest quantization (Q) level determined by the ADC in the oscilloscope. The higher the number of ADC bits, the greater the resolution. For example, an 8-bit ADC can encode an analog input to one in 256 different levels (since 2⁸ = 256), while a 10-bit ADC ideally provides four times the resolution of that (2¹⁰ = 1024 Q levels).

Vertical Scaling

Since the ADC operates on the full-scale vertical value, proper vertical scaling also helps increase oscilloscope resolution. Figure 1 shows a full screen of 800 mV (8 divisions × 100 mV/div).