#### vitoa

##### Member level 2

**AC Wheatsone bridge equivalent impedance at AC 80 MHz**

Hi, need some help to calculate equivalent impedance of this bridge and resistors needed at 80MHz

Capacitance Cx is going to be the variable.

Checking this theory

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R1/XC1 = R2/XCx at equilibrium

Cx goes from 10pF to 1nF

At 100Mhz Xc goes from 1,6ohm to 160ohms

Equivalent resistence is on this theory:

***broken link removed***

I'm going to use instrumentational amplifier to measure difference A to B. Input resistence is 1,1KOhm

So this is 1,1Kohm is equivalent to R5 in circuit.

Oscillator source can goes to minimum 500ohm impedance load. 3Vpp @ 80MHz

How to match this bridge to output of oscillator with 500ohm output impedance?