Using Features for Advanced Applications
3–162 TDS 684A, TDS 744A, & TDS 784A User Manual
Derivative waveforms are used in the measurement of slew rate of amplifiers and
in educational applications. You can store and display a derivative math
waveform in a reference memory, then use it as a source for another derivative
waveform. The result is the second derivative of the waveform that was first
differentiated.
The math waveform, derived from the sampled waveform, is computed based on
the following equation:
Yn+(X(n)1) *Xn)1
T
Where: X is the source waveform
Y is the derivative math waveform
T is the time between samples
Since the resultant math waveform is a derivative waveform, its vertical scale is
in volts/second (its horizontal scale is in seconds). The source signal is differen-
tiated over its entire record length; therefore, the math waveform record length
equals that of the source waveform.
To obtain a derivative math waveform:
1. Connect the waveform to the desired channel input and select that channel.
2. Adjust the vertical and horizontal scales and trigger the display (or press
AUTOSET).
3. Press MORE ➞ Math1, Math2, or Math3 (main) ➞ Change Math
Definition (side) ➞ Single Wfm Math (main). (See Figure 3–95).
4. Press Set Single Source to (side). Repeatedly press the same button (or use
the general purpose knob) until the channel source selected in step 1 appears
in the menu label.
5. Press Set Function to (side). Repeatedly press the same button (or use the
general purpose knob) until diff appears in the menu label.
6. Press OK Create Math Wfm (side) to display the derivative of the
waveform you input in step 1.
You should now have your derivative math waveform on screen. Use the
Vertical SCALE and POSITION knobs to size and position your waveform
as you require.
To Create a Derivative of aWaveform