HP 181A manual Measurement Definitions, Definitions of Systematic Uncertainty Terms Trigger Error

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Chapter 7 HP 53131A/132A Specifications

Measurement Definitions

Measurement Definitions

Definitions of Systematic Uncertainty Terms

•Trigger Error

External source and input amplifier noise may advance or delay the trigger points that define the beginning and end of a measurement. The resulting timing uncertainty is a function of the slew rate of the signal and the amplitude of spurious noise spikes (relative to the input hysteresis band).

The (rms) trigger error associated with a single trigger point is:

(Ein put )2 + (Esigna l)2

Trigger Error = ------------------------------------------------------------------------------------------------------ (in seconds)

Input Signal Slew Rate at Trigger Point

where

Einput = RMS noise of the input amplifier: 1 mVrms (350 μVrms typical). Note that the internal measurement algorithms significantly reduce the contribution of this term.

Esignal = RMS noise of the input signal over a 225 MHz bandwidth (100 kHz bandwidth when the low-pass filter is enabled). Note that the filter may substantially degrade the signal’s slew rate at the input of the trigger comparator.

For two-trigger-point measurements (e.g. Rise Time, Pulse Width), the Trigger Errors will be referred to independently as Start Trigger Error and Stop Trigger Error.

•Trigger Level Timing Error

Trigger level timing error results from a deviation of the actual trigger level from the specified (indicated) level. The magnitude of the measurement timing error depends on several factors, primarily: resolution and accuracy of the trigger level circuit, fidelity of the input amplifier, slew rate of the input signal at the trigger point, and width of the input hysteresis band (see illustration).

Actual Trigger Point:

Slope

0.5 Hysteresis Band

0.5 Hysteresis Band

Amplitude

Time

Upper Hystersis Limit

Trigger Level Setting

Lower Hystersis Limit

Actual Trigger Point:

Slope

Trigger Level Timing Errors

Trigger level timing error is associated with Time Interval, Pulse Width, Rise Time, Fall Time, Phase, and Duty Cycle measurements. The following equations define the general interpretation of its component error terms for a measurement. These should be summed together to obtain the overall Trigger Level Timing Error.

	0.5 × Hysteresis Band		0.5 × Hysteresis Band
Input Hysteresis: Input----------------Signal------------------Slew---------------Rate--------------at-------Start--------------Trigger---------------------Point------------ – Input-----------------Signal-----------------Slew---------------Rate--------------at-------Stop--------------Trigger--------------------Point------------
Trigger Level Setting:±	---15--------mV-----------±-----(--1%----------×-----Start---------------Trigger--------------------Level----------------Setting-------------------)---	±	---15--------mV-----------±-----(--1%----------×-----Stop--------------Trigger---------------------Level----------------Setting-------------------)--
	Input Signal Slew Rate at Start Trigger Point		Input Signal Slew Rate at Stop Trigger Point

7-12 Assembly-Level Service Guide