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Significance and DerivationAuthor: Leonard Krugman The opencircuit parameters, r_{11}, r_{12}, r_{21}, and r_{22} are used exclusively throughout this book primarily because they are the most familiar fourpole equivalents. Some engineers prefer the shortcircuit conductance parameters g_{11}, g_{12}, g_{21}, and g_{22}. The conductance parameters serve well for the junction transistor, but do not work out too well for the pointcontact type, which inherently exhibit short circuit instability.
The basic circuits for measuring the h parameters are illustrated in Fig. 710, which define the values of the parameters in terms of the input and output currents and voltages as follows: when e_{2} = 0 (output shortcircuited) when i_{1} = 0 (input opencircuited) when e_{2} = 0 (output shortcircuited) when i_{1} = 0 (input opencircuited)
Fig. 710. Basic circuits for measuring fourterminal h parameters. Notice that two of the measurements are made with the output shortcircuited, and the remaining two are made with the input opencircuited. Furthermore, none of the parameters are exact equivalents, since r_{11} is a resistance (ohms), h_{22} is a conductance (mhos), h_{12} is a numeric (voltage ratio), and h_{21} is also a numeric (current ratio).


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