circuit representation of output resistance

[sweethomela8]

Hi, I'm working with a IC that can drive a high (3.3 V) or a low (0V), it has a output impedance of 1k Ohm. That output connects to another chip with an input impedance of 10k ohm. How would one model this circuit using voltage source..resistors, gnd..etc?

 

[keith1200rs]

The output could be modeled simply as a voltage source with series 1k resistor. The input impedance is a bit more tricky as you need to makes to assumptions about the nature of the impedance. 20k to VDD and 20k to GND is one option. You probably ought to include some capacitance to ground as well.

Keith

 

[sweethomela8]

would you model the voltage source as the high voltage (3.3VDC) and low voltage (0VDC) in their on independent models based on the output?

 

[FvM]

It's very unlikely, that the chip has a constant 1k output impedance (unless it has been introduced artificially by a series resistor with low imoedance buffer). If you want a more exact simulation, you need more data or have to make assumption about the nature of the output on your own. A real device can be expected to have MOS transistors creating the output impedance, they expose a partly non-linear characteristic.