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Constant-current source circuit having a MOS transistor passing off-heat current

  • US 5,180,967 A
  • Filed: 08/22/1991
  • Issued: 01/19/1993
  • Est. Priority Date: 08/30/1990
  • Status: Expired due to Term
First Claim
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1. A constant-current source circuit having a MOS transistor passing off-leak current comprising:

  • (a) a first fixed voltage terminal having a first voltage level;

    (b) a second fixed voltage terminal having a second voltage level;

    (c) an output terminal coupled to output a constant current;

    (d) first and second nodes;

    (e) a first current mirror circuit electrically coupled between the first fixed voltage terminal and said first and second nodes, and having a first current gain, said first current mirror circuit having a first current path passing a first current from said first fixed voltage terminal to said first node and a second current path passing a second current from said first fixed voltage terminal to said second node in accordance with the first current gain;

    (f) a second current mirror circuit electrically coupled between the second fixed voltage terminal and said first and second nodes, and having a second current gain, said second current mirror circuit having a third current path passing a third current from said second node to said second fixed voltage terminal and a fourth current path passing a fourth current in accordance with the second current gain;

    (g) a current gain variation resistor coupled between the fourth current path and said second fixed voltage terminal, for controlling the fourth current to control the second current gain;

    (h) a first MOS transistor having a first conductivity type and passing a first off-leak current from said first fixed voltage terminal to said second node, the first MOS transistor including(1) a first gate electrode to which a predetermined voltage level is applied so as to keep the first MOS transistor in the off state,(2) a first electrode coupled to said first fixed voltage terminal, and(3) a second electrode coupled to said second node; and

    (i) an outputting circuit coupled between the output terminal and the first fixed voltage terminal, said outputting circuit having a control terminal coupled to the first current mirror circuit, for providing the constant current to the output terminal.

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