This is a basic differential amplifier, which is also the root for all op amps and comparitors.
Q1 is a basic constant current source. The current is split between Q2 and Q3. If one of the transistors is turned on, say Q1, then Q2 doesn't get any current, so the outputs are opposite on the collectors.
This is a non-saturated amplifier (usually), which means its speed is very fast. Op amps add a lot of gain, and have to throttle it back with internal feed back to keep themselves from oscillating. The gain of this differential amplifier is limited to the transistors Q1/Q2.
http://en.wikipedia.org/wiki/Differential_amplifier
The design is very old, and was used in the days of vacuum tubes.
Q1 is a basic constant current source. The current is split between Q2 and Q3. If one of the transistors is turned on, say Q1, then Q2 doesn't get any current, so the outputs are opposite on the collectors.
This is a non-saturated amplifier (usually), which means its speed is very fast. Op amps add a lot of gain, and have to throttle it back with internal feed back to keep themselves from oscillating. The gain of this differential amplifier is limited to the transistors Q1/Q2.
http://en.wikipedia.org/wiki/Differential_amplifier
The design is very old, and was used in the days of vacuum tubes.