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This project shows a variable bridge-T attenuator implemented with ideal resistors. It demonstrates how to access a data file which contains a table of resistor values for various attenuation states. This method of using a state table to set element parameters can be used for other variable circuits such as phase shifters.
The “Bridge_T” schematic contains the attenuator design. In it, the two resistors labeled “R1” and “R4” determine the attenuation of the circuit. The values of “R1” and “R4” are specified as a matrix in the data file “Resistor_Values”, and are easily varied by changing the variable “state” which corresponds to the attenuation states.
Referencing the Data File
The matrix represented by the data file “Resistor_Values” is assigned to variable “dfile” in the schematic “Bridge_T” using the DataFile() function:
dfile = DataFile(“Resistor_Values”)
Each row of the “dfile” matrix represents an attenuation state, and can be assigned to another variable “Rvector” using the row() function:
where “state" is an index variable corresponding to the row position in the matrix. The values of “R1” and “R4” correspond to the third and fourth column “dfile”, and also correspond to the third and fourth element of “Rvector” for each “state”:
R1 = Rvector
R2 = Rvector
By simply changing the value of “state”, the values of “R1” and “R4” are both changed concurrently.
See Text Data File Format in the Data Files Chapter of the MWO/AO/VSS User Guide for more information regarding the data file format.
The attenuation results for “state=5” is plotted on graph “Attenuation”. To see results for all attenuation states, enable the SWPVAR element.