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What it is meant by an open drain configuration of a transistor?

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hrkhari

hrkhari

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Hai Guys:

In one of the journal on VCO design, by Hajimiri, it is stated that an open drain transistors are used as drivers and are designed to drive a 50 Ohms load at 0dBm, What it is meant by an open drain configuration?.

Rgds
 

Re: Open Drain Driver

A lot of gates or comparators come with open collector outputs. That is the output pin is the collector of a transistor, the emitter is grounded, and the gate drives the base. There is NO internal pull up resistor or current source, so you add one externally. Without the external pull up, the output is zero always.

This oscillator sounds like the same thing, except that they have a fet at the output, instead of a bipolar. You would need to have an external resistor between the output and a power supply rail to get an output. Look at the data sheet for an example.
 

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