Circuital arrangement for preventing latchup in transistors with insulated collectors

Abstract

A circuital arrangement which comprises a vertical PNP transistor with insulated collector, which has a P-type collector structure surrounded by an N-type well and forms a junction therewith. In order to prevent latch-ups of the parasite SCR which is formed by the structure of the vertical transistor with insulated collector without limiting the voltage which can be applied between the collector and the emitter thereof to values below the intrinsic breakdown ones, the circuital arrangement comprises an auxiliary PNP transistor the emitter whereof is short-circuited with the emitter of the vertical PNP transistor, the base whereof is connected to the base of the vertical PNP transistor and the collector whereof is connected to the N-type well, and operates as a switch which biases the N-type well at a voltage which is close to the voltage of the emitter of the vertical PNP transistor when the latter is saturated, reverse-biasing the collector/N-well junction, and opens when the vertical PNP transistor is off, limiting. the voltage applied to the collector/N-well junction.

We claim: 
     
       1. Circuital arrangement for preventing latch-up phenomena in vertical PNP transistors with insulated collector, comprising a vertical PNP transistor with insulated collector which has its collector, base and emitter regions connected to respective terminals, said collector region, which is of the P type, being surrounded by an N-type well which forms a junction therewith, said vertical PNP transistor being driven so as to have at least one saturated on state and one off state, said circuital arrangement further comprising switch means which are interposed between said emitter region and said N-type well, said switch means being suitable for connecting said N-type well to said emitter region when said vertical PNP transistor is in the saturated on state and for opening when said vertical PNP transistor is in the off state. 
     
     
       2. Circuital arrangement according to claim 1, wherein said switch means comprise an auxiliary transistor which has its own emitter and collector terminals connected between said terminals of said vertical PNP transistor and said N-type well. 
     
     
       3. Circuital arrangement according to claim 2, wherein said auxiliary transistor is a PNP-type transistor the emitter terminal whereof is connected to the emitter terminal of the vertical PNP transistor, the base terminal whereof is connected to the base terminal of the vertical PNP transistor and the collector terminal whereof is connected to said N-type well. 
     
     
       4. Circuits arrangement according to claim 3, further comprising a resistor which is interposed between said base terminals of said vertical PNP transistor and of said auxiliary PNP transistor. 
     
     
       5. Circuital arrangement according to claim 3, wherein said auxiliary PNP transistor is integrated in an epitaxial well which is insulated with respect to said vertical PNP transistor. 
     
     
       6. A circuit arrangement for PNP transistors with junction-isolated collectors in an integrated circuit semiconductor substrate, comprising a first PNP transistor having collector, base and emitter regions surrounded by a first N-type well in said substrate; and   a second PNP transistor having collector, base and emitter regions surrounded by a second N-type well separate from said first N-type well in said substrate, said emitter region of said second PNP transistor connected to said emitter region of said first PNP transistor, said base region of said second PNP transistor connected to said base region of said first PNP transistor, and said collector region of said first PNP transistor connected to said first N-type well; whereby said first PNP transistor is prevented from latching up.     
     
     
       7. The circuit of arrangement of claim 6 further comprising a resistive means connected between said base regions of said first and second PNP transistors. 
     
     
       8. The circuit arrangement of claim 7 wherein said resistive means comprises a diffused region in said semiconductor substrate. 
     
     
       9. The circuit arrangement of claim 7 wherein said resistive means comprises a implanted region in said semiconductor substrate. 
     
     
       10. The circuit arrangement of claim 7 wherein said resistive means has a resistance value selected so that currents in said second PNP transistor are sufficiently low whereby said PNP transistor occupies a minimal area. 
     
     
       11. The circuit arrangement of claim 6 wherein said second PNP transistor is a vertical transistor. 
     
     
       12. The circuit arrangement of claim 6 wherein said second PNP transistor is a horizontal transistor. 
     
     
       13. The circuit arrangement of claim 6 wherein said first and second N-type wells are formed in an epitaxial layer on said semiconductor substrate. 
     
     
       14. A circuit arrangement of a PNP transistor in an integrated circuit semiconductor substrate, comprising a first transistor in a well of a first conductivity type in said substrate, said first transistor having a collector region of a second conductivity type in said first well, a base region of said first conductivity type in said collector region, and an emitter region of said first conductivity type in said base region; a second transistor in a second well of said first conductivity type in said substrate, said second well separated from said first well, said second transistor having a collector region of said second conductivity type in said second well, said collector region connected to said first well, a base region of said first conductivity type connected to said base region of said first transistor, and a emitter region of said second conductivity type connected to said emitter region of said first transistor; whereby said first transistor is prevented from latching up. 
     
     
       15. The circuit arrangement as in claim 14 further comprising resistive means connected between said base regions of said first and second transistors. 
     
     
       16. The circuit arrangement as in claim 15 wherein said first transistor is a power transistor and said second transistor is an auxiliary transistor occupying minimal area in said substrate. 
     
     
       17. The circuit arrangement as in claim 16 wherein said first conductivity type is N-type and said second conductivity type .[.in.]. is P-type. 
     
     
       18. The circuit arrangement as in claim 15 wherein said resistive means comprises a resistor having a value such that currents in said second transistor are sufficiently low whereby said second transistor can occupy a minimal area in said substrate. 
     
     
       19. The circuit arrangement as in claim 18 wherein said resistor comprises a diffused resistor. 
     
     
       20. The circuit arrangement as in claim 18 wherein said resistor comprises an implanted resistor. .Iadd. 
     
     
       21.  A circuit for preventing latch-up in a first PNP transistor having an emitter, a base, and a collector formed within an N-type region, the circuit comprising: a second PNP transistor having an emitter and a base respectively coupled to the emitter and the base of the first PNP transistor and having a collector coupled to the N-type region..Iaddend..Iadd.22. The circuit of claim 21, wherein the first PNP transistor is a vertical PNP transistor..Iaddend..Iadd.23. The circuit of claim 21, wherein the N-type region is an N-type well, and the first transistor is formed within the N-type well..Iaddend..Iadd.24. The circuit of claim 21, further comprising a resistor coupled between the bases of the first and second PNP transistors..Iaddend..Iadd.25. The circuit of claim 24, wherein the resistor has a value that is sufficiently great to limit a current that flows in the second PNP transistor..Iaddend..Iadd.26. The circuit of claim 21, wherein the first and second PNP transistors are both formed within an integrated circuit..Iaddend..Iadd.27. The circuit of claim 26, wherein the first and second PNP transistors each has an area, and the area of the first PNP transistor combined with the area of the second PNP transistor is not substantially greater than the area of the first PNP transistor   
     
     
        alone..Iaddend..Iadd.28.  The circuit of claim 26, wherein the second PNP transistor is formed within a separate well that is electrically insulated from the N-type region in which the first PNP transistor is formed..Iaddend..Iadd.29. The circuit of claim 26, wherein the second PNP transistor is a lateral PNP transistor..Iaddend..Iadd.30. The circuit of claim 26, wherein the second PNP transistor is a vertical PNP transistor..Iaddend..Iadd.31. The circuit of claim 26, wherein a resistor coupled between the bases of the first and second PNP transistors is formed within the integrated circuit as a diffused resistor..Iaddend..Iadd.32. The circuit of claim 26, wherein a resistor coupled between the bases of the first and second PNP transistors is formed within the integrated circuit as an implanted resistor..Iaddend..Iadd.33. An integrated circuit protected against latch-up, comprising: a first PNP transistor having an emitter, a base, and a collector coupled to an N-type region; and   a second PNP transistor having an emitter and a base respectively coupled to the emitter and the base of the first PNP transistor and having a collector coupled to the N-type region..Iaddend..Iadd.34. The circuit of claim 33, wherein the first PNP transistor is a vertical PNP transistor..Iaddend..Iadd.35. The circuit of claim 33, wherein the N-type region is an N-type well, and the first transistor is formed within the   
     
     
        N-type well..Iaddend..Iadd.36.  The circuit of claim 33, further including a resistor coupled between the bases of the first and second PNP transistors..Iaddend..Iadd.37. The circuit of claim 36, wherein the resistor is a diffused resistor..Iaddend..Iadd.38. The circuit of claim 36, wherein the resistor is an implanted resistor..Iaddend..Iadd.39. The circuit of claim 36, wherein the resistor has a value that is sufficiently great to limit a current that flows in the second PNP transistor..Iaddend..Iadd.40. The circuit of claim 33, wherein the first and second PNP transistors each has an area, and the area of the first PNP transistor combined with the area of the second PNP transistor is not substantially greater than the area of the first PNP transistor alone..Iaddend..Iadd.41. The circuit of claim 33, wherein the second PNP transistor is formed in a separate well that is electrically insulated from the N-type region in which the first PNP transistor is formed..Iaddend..Iadd.42. The circuit of claim 33, wherein the second PNP transistor is a lateral PNP transistor..Iaddend..Iadd.43. The circuit of claim 33, wherein the second PNP transistor is a vertical PNP 
     
     
        transistor..Iaddend..Iadd.44.  A circuit for preventing latch-up in a first PNP transistor having an emitter, a base, and a collector coupled to an N-type region, the circuit comprising: a switch having a first terminal coupled to the emitter and a second terminal coupled to the N-type region, said switch being closed in response to a forward bias from the emitter to the base of the first PNP transistor..Iaddend..Iadd.45. The circuit of claim 44, wherein the switch is opened in response to the forward bias being removed from the emitter to the base of the first PNP transistor..Iaddend..Iadd.46. The circuit of claim 44, wherein the switch includes a second transistor having an emitter coupled to the first terminal and a collector coupled to the second terminal..Iaddend..Iadd.47. The circuit of claim 46, wherein the second transistor is a second PNP transistor further having a base, and the base of the second PNP transistor is coupled to the base of the first PNP transistor..Iaddend..Iadd.48. The circuit of claim 47, further including a resistor coupled between the base of the first PNP transistor and the base of the second PNP transistor..Iaddend..Iadd.49. A circuit for preventing latch-up in a PNP transistor having an emitter, a base, and a collector coupled to an N-type region, the circuit comprising:   switching means for selectively connecting the emitter of the PNP transistor and the N-type region in response to a bias voltage between the emitter and the base of the PNP transistor crossing a predetermined voltage..Iaddend..Iadd.50. The circuit of claim 49, wherein the switching means connects the emitter of the PNP transistor and the N-type region in response to the bias voltage exceeding the predetermined voltage, and disconnects the emitter of the PNP transistor and the N-type region in response to the bias voltage falling below the predetermined voltage..Iaddend..Iadd.51. The circuit of claim 50, wherein the PNP transistor has a forward biased emitter-base voltage drop, and the predetermined voltage substantially equals the forward biased emitter-base voltage drop..Iaddend..Iadd.52. A method for preventing a latch-up condition in a PNP transistor having an emitter, a base, and a collector, the collector being contiguous with an N-type region, the method comprising the steps of:   A. detecting whether a forward bias condition exists from the emitter to the base of the PNP transistor; and   B. selectively coupling the emitter of the PNP transistor to the N-type region in response to step A..Iaddend..Iadd.53. The method of claim 52, wherein step B includes the steps of:   C. coupling the emitter of the PNP transistor to the N-type region in response to a detection in step A that a forward bias exists; and   D. decoupling the emitter of the PNP transistor from the N-type region in response to a detection in step A that no forward bias condition exists..Iaddend.