Device for generating a reference voltage for a switching circuit including a capacitive bootstrap circuit

Abstract

This device for generating a reference voltage for a capacitive bootstrap circuit of an output stage can be easily integrated. The output stage comprises a driving block, a capacitive bootstrap circuit and a reference voltage generating block generating a floating reference voltage which is referred to the output voltage signal and switches in accordance thereto.

We claim: 
     
       1. In a circuit including a driving block having an input receiving an input switching signal and an output generating a switching output voltage signal which switches between a low level and a high level, and a capacitive bootstrap circuit having a fast terminal connected to said output of said driving block and a second terminal, a device for generating a floating reference voltage is connected between said output of said driving block and said second terminal of said capacitive bootstrap circuit, said device generating said floating reference voltage so as to follow said switching output voltage signal and avoid damage to said bootstrap circuit, said floating reference voltage switching to a low state, higher than said low level of said switching output voltage signal for charging said capacitive bootstrap circuit, when said switching output voltage signal switches to said low level, said floating reference voltage switching to a high state, near to said high level, when said switching output voltage signal switches to said high level. 
     
     
       2. In a circuit including a driving block having an input receiving an input switching signal and an output generating a switching output voltage signal, and a capacitive bootstrap circuit having a first terminal connected to said output of said driving block and a second terminal, a device for generating a floating reference voltage is connected between said output of said driving block and said second terminal of said capacitive bootstrap circuit, said floating reference voltage switching in accordance with said switching output voltage signal, wherein said device comprises Zener diode means having an anode and a cathode, said anode being connected to said output of said driving block, and a transistor having a source and a gate terminal; said gate terminal being connected to said cathode of said Zener diode means and to a reference potential line through first resistor means, said source terminal being connected to said second terminal of said capacitive bootstrap circuit and to said output of said driving block through control means controlling switching on and off of said transistor. 
     
     
       3. A device according to claim 2, wherein said control means for said transistor comprises further resistor means. 
     
     
       4. A device according to claim 2, wherein said capacitive bootstrap circuit defines a feedback connection interposed between said source terminal of said transistor and said output of said driving block, said bootstrap circuit including a further diode having an anode connected to said source terminal of said transistor and a cathode connected to said output through a bootstrap capacitor. 
     
     
       5. A device according to claim 2, wherein said transistor is a MOS transistor. 
     
     
       6. A device according to claim 2, wherein said Zener diode means comprises a plurality of Zener diodes connected in series. 
     
     
       7. A device according to claim 2, wherein said control means for said transistor comprise current source means. 
     
     
       8. A device according to claim 2, wherein said transistor is an NPN-type bipolar transistor. 
     
     
       9. An output stage, comprising a driving block interposed between a first reference potential line and a second reference potential line, said driving block having a signal input receiving an input switching signal, a reference input connected to a further reference potential line and an output generating an output switching signal which switches between a low level that is substantially equal to said second reference potential line and a high level that is substantially equal to said first potential reference line, and a capacitive bootstrap circuit connected between said output of said driving block and said further reference potential line, said stage including means for generating a floating reference voltage connected to said further reference potential line, said means generating said floating reference voltage so as to follow said output switching signal and avoid damage to said bootstrap circuit said floating reference voltage switching to a low state, higher than said low level of said switching output voltage signal for charging said capacitive bootstrap circuit, when said switching output voltage signal switches to said low level, said floating reference voltage switching to a high state, near to said high level, when said switching output voltage signal switches to said high level. 
     
     
       10. In a circuit including a driving block having an input receiving an input switching signal and an output generating a switching output voltage signal, said switching output voltage signal switching between a low level and a high level, and a capacitive bootstrap circuit having a first terminal connected to said output of said driving block and a second terminal, a device for generating a floating reference voltage is connected between said output of said driving block and said second terminal of said capacitive bootstrap circuit, said floating reference voltage switching to a low state for charging said capacitive bootstrap circuit when said switching output voltage signal switches to said low level, said low state being higher than said low level of said switching output voltage signal, and said floating reference voltage switching to a high state, when said switching output voltage signal switches to said high level, said high state being near to said high level, wherein said device comprises Zener diode means having an anode and a cathode, said anode being connected to said output of said driving back, and a transistor having a source and a gate terminal, said gate terminal being connected to said cathode of said Zener diode means and to a reference potential line through first resistor means, said source terminal being connected to said second terminal of said capacitive bootstrap circuit and to said output of said driving block through control means controlling switching on and off of said transistor. 
     
     
       11. An output stage, comprising a driving block interposed between a first reference potential line and a second reference potential line, said driving block having a signal input receiving an input switching signal, a reference input connected to a further reference potential line and an output generating an output switching signal which switches between a low level that is substantially equal to said second reference potential line and a high level that is substantially equal to said first potential reference line, and a capacitive bootstrap circuit including a bootstrap diode, said bootstrap circuit being connected between said output of said driving block and said further reference potential line, said stage including means for generating a floating reference voltage connected to said further reference potential line, said means generating said floating reference voltage so as to follow said output switching signal and minimize inverse bias voltage on said bootstrap diode, raid floating reference voltage switching to a low state, higher than said low level of said switching output voltage signal for charging said capacitive bootstrap circuit, when said switching output voltage signal switches to said low level, said floating reference voltage switching to a high state, near to said high level, when said switching output voltage signal switches to said high level. .Iadd.12. In a circuit including a driving block having an input receiving an input switching signal and an output generating a switching output voltage signal which switches between a low level and a high level, and a capacitive bootstrap circuit having a first terminal connected to said output of said driving block and a second terminal, a device for generating a floating reference voltage is connected between said output of said driving block and said second terminal of said capacitive bootstrap circuit, said device generating said floating reference voltage so as to follow said switching output voltage signal and avoid damage to said bootstrap circuit, said floating reference voltage switching to a low state, higher than said low level of said switching output voltage signal for charging said capacitive bootstrap circuit when said switching output voltage signal switches to said low level, and said floating reference voltage switching to a high state when said switching output voltage signal switches to said high level. 
     
     
        .Iaddend..Iadd.13.  In a circuit including a driving block having an input receiving an input switching signal and an output generating a switching output voltage signal, and a capacitive bootstrap circuit having a first terminal connected to said output of said driving block and a second terminal, a device for generating a floating reference voltage is connected between said output of said driving block and said second terminal of said capacitive bootstrap circuit, said floating reference voltage switching in accordance with said switching output voltage signal, wherein said device comprises a zener diode having an anode and cathode, said anode being connected to said output of said driving block, and a transistor having an output terminal and a control terminal, said control terminal being connected to said cathode of said zener diode and to a reference potential line through at least one resistor, said output terminal being connected to said second terminal of said capacitive bootstrap circuit and to said output of said driving block through control means controlling switching on and off of said transistor. 
     
     
        .Iaddend..Iadd. 4.  A bootstrap circuit for boosting an input signal of a drive transistor, the drive transistor including a first terminal coupled to a supply voltage, a second terminal providing an output of the drive transistor, and a third terminal receiving the input signal from a driving element, the driving element having an input and an output that provides the input signal to the third terminal of the drive transistor, the bootstrap circuit comprising: a diode having a cathode terminal and an anode terminal;   a capacitor, having a first terminal coupled to the cathode terminal of the diode, and a second terminal coupled to the second terminal of the drive transistor; and   means for providing a bootstrap reference voltage to the anode terminal of the diode that limits an inverse bias voltage of the diode. .Iaddend..Iadd.15. A bootstrap circuit for boosting an input signal of a drive transistor, the drive transistor including a first terminal coupled to a supply voltage, a second terminal providing an output of the drive transistor, and a third terminal receiving the input signal from a driving element, the driving element having an input and an output that provides the input signal to the third terminal of the drive transistor, the bootstrap circuit comprising:   a bootstrap diode having a cathode terminal and an anode terminal;   a capacitor, having a first terminal coupled to the cathode terminal of the bootstrap diode, and a second terminal coupled to the second terminal of the drive transistor; and   a bootstrap reference voltage generator, having a first input coupled to the supply voltage, a second input coupled to the second terminal of the drive transistor, and an output coupled to the anode terminal of the bootstrap diode. .Iaddend..Iadd.16. The bootstrap circuit of claim 15, wherein:   the bootstrap diode has an inverse bias voltage when a voltage at the cathode terminal of the bootstrap diode is greater than a voltage at the anode terminal of the bootstrap diode; and   the output of the bootstrap reference voltage generator limits the inverse   
     
     
        bias voltage of the bootstrap diode. .Iaddend..Iadd.17.  The bootstrap circuit of claim 15, wherein the bootstrap reference voltage generator comprises: a bootstrap transistor, having a first terminal coupled to the supply voltage, a second terminal providing the output of the bootstrap reference voltage generator, and a third terminal;   a first resistive element, coupled between the supply voltage and the third terminal of the bootstrap transistor;   a second resistive element, coupled between the second terminal of the bootstrap transistor and the second input of the bootstrap reference voltage generator; and   a Zener diode having a cathode terminal coupled to the third terminal of the bootstrap transistor and an anode terminal coupled to the second input of the bootstrap reference voltage generator. .Iaddend..Iadd.18. The bootstrap circuit of claim 17, wherein the bootstrap transistor is a MOS transistor. .Iaddend..Iadd.19. The bootstrap circuit of claim 17, wherein the bootstrap transistor is a bipolar transistor. .Iaddend..Iadd.20. The bootstrap circuit of claim 17, wherein the Zener diode is at least two   
     
     
        zener diodes connected in series. .Iaddend..Iadd.21.  A reference voltage generator for providing a bootstrap reference voltage to a bootstrap circuit, the bootstrap reference voltage being generated from a supply voltage and an input voltage, the reference voltage generator comprising: a bootstrap transistor, having a first terminal coupled to the supply voltage, a second terminal providing the bootstrap reference voltage, and a third terminal;   a first resistive element, coupled between the supply voltage and the third terminal of the bootstrap transistor;   a second resistive element, coupled between the second terminal of the bootstrap transistor and the input voltage; and   a Zener diode having a cathode terminal coupled to the third terminal of the bootstrap transistor and an anode terminal coupled to the input voltage. .Iaddend.