What is the Variable Baseline option 001 of the 8114A?

In a standard 8114A, the baseline is fixed at 0 V. The output pulses are positive or negative of this baseline according to polarity selected. To have a variable baseline from -25 V to +25 V, the 8114A must be fitted with option 001. The output signal can go positive or negative from the baseline.

The output window for the 8114A is +50 V to -50 V (50-Ohm into 50-Ohm). Therefore, the position of the baseline can limit the maximum available amplitude, depending on the output polarity selected. For example, if the baseline is set at +20 V, the output amplitude can be varied up to a positive limit of 30 V, but to a negative limit of 50 V.

In addition to output window, the maximum available output amplitude may also be limited by the duty cycle (pulse width) settings. Refer to Figure 1 and Figure 2.

Figure 1 shows the maximum possible duty cycle for a given pulse amplitude from 50-Ohm into 50-Ohm. Note that the amplitude doubles from High-Z into 50-Ohm.

Refer to Figure 2. Under the following conditions, Figure 1 still applies for maximum duty cycle:

• Positive pulse with negative baseline
• Negative pulse with positive baseline
• 5 V <= Baseline <= +5 V, negative or positive pulses

Under the following conditions, maximum duty cycle is 15%:

• Baseline > + 5V and positive pulses
• Baseline < -5V and negative pulses