Low di/dt BiCMOS output buffer with improved speed
First Claim
1. An output buffer comprising:
- a voltage regulator, coupled to first and second power supply voltage terminals, for providing a regulated voltage characterized as having a constant voltage substantially independent of fluctuations in voltage between said first power supply voltage terminal and said second power supply voltage terminal;
first and second current sources, each coupled to said voltage regulator, for providing first and second currents from said voltage regulator, respectively, to first and second nodes;
switching means, coupled to said first and second current sources, for providing voltage signals at said first and second nodes respectively in response to positive and negative voltage differences between first and second input voltages;
a third current source, having a first terminal coupled to said switching means, and a second terminal coupled to said second power supply voltage terminal;
output means, coupled to said first and second nodes, for providing an output signal at a logic high voltage in response to said voltage signal at said first node, and for providing said output signal as a logic low voltage in response to said voltage signal at said second node.
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Abstract
An output buffer for a device such as a memory comprises a voltage regulator, a current source portion, a switching portion, and an output portion. The voltage regulator provides a constant voltage independent of fluctuations between first and second power supply voltages. The current source portion provides first and second currents to first and second nodes to limit the rate at which transistors in the output portion become conductive. The switching portion provides voltage signals on the first and second nodes respectively in response to positive and negative voltage differences between first and second input voltages. The output portion provides an output signal at either a logic high or a logic low voltage respectively in resonse to the voltage signals at the first and second nodes. The current source portion allows the use of faster bipolar transistors to improve the speed of the output buffer while maintaining accepable di/dt.
30 Citations
22 Claims
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1. An output buffer comprising:
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a voltage regulator, coupled to first and second power supply voltage terminals, for providing a regulated voltage characterized as having a constant voltage substantially independent of fluctuations in voltage between said first power supply voltage terminal and said second power supply voltage terminal; first and second current sources, each coupled to said voltage regulator, for providing first and second currents from said voltage regulator, respectively, to first and second nodes; switching means, coupled to said first and second current sources, for providing voltage signals at said first and second nodes respectively in response to positive and negative voltage differences between first and second input voltages; a third current source, having a first terminal coupled to said switching means, and a second terminal coupled to said second power supply voltage terminal; output means, coupled to said first and second nodes, for providing an output signal at a logic high voltage in response to said voltage signal at said first node, and for providing said output signal as a logic low voltage in response to said voltage signal at said second node. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An output buffer coupled to first and second power supply voltage terminals comprising:
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input means for either, providing first and second signals in response to a voltage difference between true and complementary input voltages, or for providing said first and second signals at the second power supply voltage in response to a select signal; clamp means, coupled to said input means, for clamping said first and second signals at a first predetermined minimum voltage; a level shifter, coupled to said input means, for providing third and fourth signals respectively at voltages of said first and second signals minus a predetermined voltage; feedback means, coupled to said level shifter, for maintaining said first and third signals at a second predetermined minimum voltage in response to said select signal; pullup means for providing a fifth output signal in response to said third signal; and output stage means for providing a data output signal at a data output node, said output stage means providing said data output signal at a logic high voltage in response to at least one of said third signal and said fifth signal, and for providing said data output signal at a logic low voltage in response to said fourth signal. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19)
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20. An output buffer comprising:
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input means for providing first and second signals respectively in response to positive and negative voltage differences between true and complementary input voltages, a logic high voltage of said first and second signals equal to a first predetermined voltage; pullup means for providing a third signal in response to said first signal, a logic high voltage of said third signal equal to a second predetermined voltage; a first transistor having a collector coupled to a first power supply voltage terminal, a base for receiving said first signal, and an emitter for providing a data output signal of the output buffer; a second transistor having a collector coupled to said first power supply voltage terminal, a base for receiving said third signal, and an emitter; a resistor having a first terminal coupled to said emitter of said second transistor, amd a second terminal coupled to said emitter of said first transistor; and a third transistor having a first current electrode coupled to said emitter of said first transistor, a control electrode for receiving said second signal, and a second current electrode coupled to a second power supply voltage terminal. - View Dependent Claims (21, 22)
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Specification