Current switch with bipolar switching transistor and .beta. compensating circuit

A current switch, comprising:

• at least one switching transistor having a collector electrode for coupling to a first voltage source, an emitter electrode, a base electrode for receiving a control signal, and a current gain .beta., said at least one switching transistor responsive to said control signal to turn on to produce a collector current;
• and
• a bias circuit for causing said collector current to have a predetermined value when said at least one switching transistor is on, said bias circuit including:
• first and second transistors having base electrodes coupled in common, said first transistor having a collector electrode coupled to the emitter electrode of said at least one switching transistor and an emitter electrode for coupling to a second voltage source, said second transistor having a collector electrode for coupling to a current source and an emitter electrode for coupling to said second voltage source;
• and
• a compensating circuit coupled to the emitter electrode of said at least one switching transistor for reducing the dependence of said collector current of said at least one switching transistor on said current gain 62 , said compensating circuit including a third transistor having a collector electrode coupled to the emitter electrode of said at least one switching transistor, an emitter electrode coupled to the base electrode of said first transistor, and a base electrode coupled to the collector electrode of said second transistor.

A current switch, comprising:

• at least one switching transistor having a collector electrode for coupling to a first voltage source, an emitter electrode, and a base electrode for receiving a control signal, said at least one switching transistor responsive to said control signal to turn on to produce a collector current;
• and
• a bias circuit for causing said collector current to have a predetermined value when said at least one switching transistor is on, said bias circuit including:
• first and second transistors having base electrodes coupled in common, said first transistor having a collector electrode coupled to the emitter electrode of said at least one switching transistor and an emitter electrode for coupling to a second voltage source, said second transistor having a collector electrode for coupling to a current source and an emitter electrode for coupling to said second voltage source;
• and
• a third transistor having a drain electrode coupled to the emitter electrode of said at least one switching transistor, a source electrode coupled to the base electrode of said first transistor, and a gate electrode coupled to the collector electrode of said second transistor.

A current switch, comprising:

• at least one switching transistor having a collector electrode for coupling to a first voltage source, an emitter electrode, a base electrode for receiving a control signal, and a current gain .beta., said at least one switching transistor responsive to said control signal to turn on to produce a collector current;
• and
• a bias circuit for causing said collector current to have a predetermined value when said at least one switching transistor is on, said bias circuit including:
• first and second transistors having base electrodes coupled in common, said first transistor having a collector electrode coupled to the emitter electrode of said at least one switching transistor and an emitter electrode for coupling to a second voltage source, said second transistor having a collector electrode for coupling to a current source and an emitter electrode for coupling to said second voltage source:
• and
• a compensating circuit coupled to the emitter electrode of said at least one switching transistor for reducing the dependence of said collector current of said at least one switching transistor on said current gain .beta., said compensating circuit including a third transistor having a drain electrode coupled to the emitter electrode of said at least one switching transistor, a source electrode coupled to the base electrode of said first transistor, and a gate electrode coupled to the collector electrode of said second transistor.