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Hi, I've been struggling with this problem for about an hour and I just don't know how to determine the transfer function for this circuit. My first attempt was analysing how the circuit behaves when the input is positive but I couldn't get to any reasonable result. I've also made the analysis when the the input is zero by setting up two loops sharing the test load (the one that is connected to vo).

I don't know if you could point into the right direction.

  • \$\begingroup\$ Describe the direction you are thinking of first. You have to show some effort. \$\endgroup\$
    – Eugene Sh.
    Mar 27, 2015 at 15:30
  • \$\begingroup\$ Did you add the 10k ohm on the output or is that part of the original problem. Without the 10k I'd first assume no currents into/ out of Vin and Vout. And then a simple diode model (no conduction below ~0.5V and perfect conduction above that... sorta perfect switches.) \$\endgroup\$ Mar 27, 2015 at 16:29
  • \$\begingroup\$ My instructor added the resistor, claiming that it will be easier that way \$\endgroup\$
    – avm
    Mar 27, 2015 at 16:50

2 Answers 2


This is a 4-diode sampling bridge as used in sampling oscilloscopes. With the +/-10V as shown the output follows the input. If the polarities of the bias voltages are reversed the output is disconnected from the input.

In sampling oscilloscope use the output will have a small capacitor rather than a resistor to hold the sample value.

The bridge can do very fast sampling of the order of picoseconds if needed giving extremely the bandwidths.

With the input at zero the same current flows through both legs of the circuit and the output voltage will also be zero, any variation of the input voltage requires that output voltage follow the input to maintain equilibrium.



This circuit is effectively a limiter. You will find 3 distinct regions of operation. In the middle zone the output follows the output. You will need to calculate the transition points and figure out what happens outside the middle zone- we can't do your homework for you. You can start by looking at what happens with inputs of -10/0/+10 and then figure out what happens in between.


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