simon2
Junior Member
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Posts: 27
Southampton, United Kingdom.
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No. Use:
.SUB Gyrator (Pin Nin Pout Nout)
*--------------------------------------------- * Pin o---o--o--- ----o Pout * | | |_ | * Rp | _Ef * | | | | * | | | Rs * | | | | * | Fr~~~~~Vs * | | | | * Nin o---o--o--- ----o Nout *---------------------------------------------
Rp Pin Nin 10Meg Ef Pout 5 Pin Nin 1 Rs 5 6 1u Vs 6 Nout 0 Fr Nin Pin Vs 1 .ENDS Gyrator
which is a simple 1:1 isolation bi-directional transformer. The voltage controlled voltage source implements the "forward" path, whereas the current controlled current source implements the "reverse" path, both are completely independent of the other; a simple explanation is that a voltage applied at the left appears at the right resulting in a current through the load on the right, which is reflected back to the left such that an impedance on the right appears electrically on the left. The input and output common mode levels are completely isolated and the structure works to DC.
For a realistic "balun" use a transformer with one side centre-tapped thus:
*** Centre-tapped 2:1 matching transformer:
.SUBCKT Tx2CT21 (GND PP PCT PN SP SN)
.PARAM Lp=1u n=2 Ll=1n K=0.96 Cw=2p *--------------------------------------------- * PP o---o-Cl/2-- * | | * Lp/2 o---o SP * | | * PCTo---o Ls * | | * Lp/2 o---o SN * | | * PN o---o-Cl/2-- *---------------------------------------------
Xoutpp PP PCT SP SN Gyrator1 Xoutpn PCT PN SP SN Gyrator1
Ls S SN {Lp*n^2} Ll SP S {(1-K)*Lp*n^2}
CPSp PP SP {Cw/2} CPSn PN SN {Cw/2}
.SUBCKT Gyrator1 1 2 3 4 *--------------------------------------------- * 1 o---o--o--- ----o 3 * | | |_ | * Rp | _Ef * | | | | * | | | Rs * | | | | * | Fr~~~~~Vs * | | | | * 2 o---o--o--- ----o 4 *--------------------------------------------- Rp 1 2 10Meg Ef 3 5 1 2 {n} Rs 5 6 1u Vs 6 4 0 Fr 2 1 Vs {n} .ENDS Gyrator1
.ENDS Tx2CT21CT
You will probably have to put the netlists as a text file into Wordpad to view the text "diagrams" properly .... the example is for a Mini-circuits centre-tapped 2:1 balun typically used for an unbalanced 50 ohm line to a balanced 100 ohm line as used in the VHF and lower UHF bands. The syntax is for WinSPICE, you may have to change .subckt to .sub and change the curly brackets { } to single quotes ' ' around the expressions for Hspice and Spectre. Some versions of SPICE may not like the gyrator subcircuit nested inside the transformer sub-circuit. Other versions may not like the n^2, but rather prefer n** or n*n. Notice that n sets the turns ratio and therefore the impedance that will appear from one side to the other.
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