Agilent Technologies 4294A Specifications download pdf (Page 109)

Figure 5-44. Equivalent circuit models

If the simulated frequency response curve partially fits the measurement results, it can be said that

the selected circuit mode is proper only for that part of the frequency range that it fits. Figure 5-45

(a) shows an example measurement for a low value inductor. As shown in Figures 5-45 (b) and (c),

the measurement result does not agree with both the simulated curves over the full frequency range.

The higher frequency region is well simulated by circuit mode A and the lower frequency region by

circuit mode B. In other words, the circuit mode for the inductor is like the circuit mode A at the

higher frequencies and like circuit mode B at lower frequencies. At lower frequencies L is the domi-

nant element, circuit mode A describes the response curve best. At the higher frequencies L and R

are the dominant circuit elements, circuit B describes the response curve best. From these facts, we

can determine that the real circuit mode should be the combination of circuit modes A and B, and is

like Figure 5-46 (a). Figure 5-46 (b) lists an I-Basic program to simulate the frequency response for

the circuit given in Figure 5-46 (a). The value of Rs should be keyed in from the front panel and

entered into the internal register, and then calculation is executed to see the simulated curve. In

this example, the simulated curve agreed with the actual result as shown in Figure 5-46 (c) when the

value of Rs is 1 Ω.

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Agilent Technologies 4294A Specifications Page 109