Bipolar transistor switching enhancement circuit
AssigneeFairchild Semiconductor Corporation
InventorsJames R. Kuo, Brian R. Carey, Timothy G. Moran
Life of this patent
Estimating the term…
Abstract
A line driver circuit capable of operating at high speeds. The output transistor, an emitter connected to an output terminal, has a special feedback capacitor connected to its base. The feedback capacitor helps pull the output terminal high to increase the switching speed of the line driver circuit. Special current injection and removal techniques are used to speed the switching times of the PNP current supply transistors. The line driver circuit also has special circuitry to limit the output current from exceeding certain limits and for keeping the line driver circuit from overheating.
Claims17
A circuit for turning on at least one PNP transistor at high speed comprising:
- switching means responsive to an input signal for biasing said PNP transistor to turn on said transistor,
- a first transistor having a base terminal coupled to said switching means such that said first transistor turns off when said switching means turns said PNP transistor on, a collector terminal coupled to a first voltage supply through a further switching means and a base region of said PNP transistor, and an emitter terminal coupled to a second voltage supply, and
- capacitive means connected between said base and collector terminals of said first transistor,
- whereby said capacitive means turns said first transistor momentarily on when said switching means turns on said PNP transistor to create a current surge from said base region of said PNP transistor.
A circuit for turning on at least one PNP transistor at high speed comprising:
- switching means for biasing said PNP transistor to turn on said transistor,
- a first transistor having a base terminal coupled to said switching means, a collector terminal coupled to a first voltage supply through a bias means, said collector terminal also coupled to a base region of said PNP transistor and an emitter terminal coupled to a second voltage supply so that responsive to said switching means said first transistor drives current from said base region of said PNP transistor when said switching means turns on said PNP transistor, and
- means coupled to said PNP transistor and to said first transistor for turning off first transistor after the PNP transistor is turned on,
- whereby said PNP transistor is turned on by a temporary current surge from said base region of said PNP transistor base region after said switching means first turns on said PNP transistor.
A circuit for turning off at least one PNP transistor at high speed comprising:
- switching means responsive to an input signal for biasing said PNP transistor on and for unbiasing said PNP transistor off,
- a first transistor having a base terminal coupled to said switching means such that said first transistor turns off when said switching means turns said PNP transistor off, a collector terminal coupled to a first voltage supply through a further switching means, and an emitter terminal coupled to a second voltage supply,
- a second transistor having a base terminal coupled to said first transistor collector terminal, an emitter terminal coupled to said first voltage supply, and a collector terminal coupled to a base region of said PNP transistor, and
- capacitive means connected between said base and collector terminals of said first transistor, said capacitive means turning said first transistor momentarily on when said switching means unbiases said PNP transistor, said first transistor momentarily turning said second transistor on,
- whereby said second transistor generates a current to said base region of said PNP transistor.
Dependencies are inferred from the claim text.