Teledyne LeCroy LabMaster 9Zi-A - Manual (Page 125)

Getting Started Manual
922157-00 Rev A 117
Response Optimization Modes
Frequency response and group delay of the oscilloscope contributes to the
pulse response characteristics of the oscilloscope. By slightly adjusting
these characteristics using digital signal processing, the characteristic
response of the oscilloscope can be optimized for your specific application.
Frequency response is defined as the decrease in the magnitude response
with respect to frequency. A fourth-order Bessel roll-off slightly attenuates
the frequencies near the bandwidth rating of the oscilloscope while a brick-
wall frequency response passes slightly higher frequency content.
Group delay is defined as the rate of change of the total phase shift with
respect to angular frequency through a device or transmission medium.
Amplifiers in analog oscilloscopes typically have some group delay at the
highest frequencies. This inherent group delay minimizes the preshoot
present on a step response and provides the traditional pulse response
with no preshoot before the step. When zero group delay is provided at all
frequencies, preshoot and overshoot is equalized.
Teledyne LeCroy provides three choices for Response Optimization Mode
selection. These choices combine a frequency and group delay response to
optimize the oscilloscope for particular applications.

Pulse Response - A group delay compensation minimizing preshoot,
this selection most resembles the response of an analog oscilloscope
by controlling group delay to be slightly non-zero at the highest
frequencies. In addition, a fourth-order Bessel frequency response is
implemented.

Eye Diagram - Flat group delay compensation resulting in equalized
preshoot and overshoot. This selection improves the symmetry of
serial eye diagrams. In addition, a fourth-order Bessel frequency
response is implemented.