US 5,311,077 AGranted

Power supply, temperature, and load capacitance compensating, controlled slew rate output buffer

AssigneeNational Semiconductor Corporation

InventorMichael A. Brown

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Abstract

A controlled slew rate output buffer has an input stage that generates a charging current in response to the rising edge of an input signal and that generates a discharging current in response to the falling edge of the input signal so that both the charging current and the discharging current are substantially constant over a temperature range and a power supply voltage range. A charging stage responds to the charging current by charging an intermediate node at a first slew rate that is substantially constant over the temperature range and the power supply voltage range. A discharging stage responds to the discharging current by discharging the intermediate node at a second slew rate that is substantially constant over the temperature range and the power supply voltage range. A charging output stage responds to the charging of the intermediate node and charges an output node at a third slew rate that is substantially equivalent to the first slew rate and that is substantially constant over the temperature range, the power supply voltage range, and an output capacitance range. A discharging output stage responds to the discharging of the intermediate node and discharges the output node at a fourth slew rate that is substantially equivalent to the second slew rate and that is substantially constant over the temperature range, the power supply voltage range, and the output capacitance range.

Claims28

Dependent claims

A controlled slew rate output buffer that repeats an input signal to an output node of the output buffer, the input signal transitioning from a low voltage level to a high voltage level and transitioning from the high voltage level to the low voltage level, the output buffer comprising:

(a) an input stage that includes a charging leg and a discharging leg that respond to the input signal by alternately providing a current path for a fixed current from a power supply to a current source;
(b) a charging stage that responds to the current in the charging leg of the input stage by charging a first node to the high voltage at a rising slew rate that is substantially determined by a magnitude of a first charging current and a capacitance of a capacitor;
(c) a discharging stage that responds to current in the discharging leg of the input stage by discharging the first node to an intermediate low voltage at a falling slew rate that is substantially equivalent to the rising slew rate of the first node wherein the rising slew rate and the falling slew rate of the first node are substantially constant over a specified temperature range, a specified power supply range, a specified capacitive loading range, and with substantially equal rising and falling slew rates;
(d) a hold-down stage connected to the first node and that responds to the discharge of the first node to the intermediate low voltage by pulling the first node down to the low voltage and by pulling the output node down to a final low voltage;
and
(e) an output stage connected between the first node and the output node for tracking the rising slew rate and the falling slew rate at the first node during the charging and discharging of the first node such that a rising slew rate and a falling slew rate of an output signal at the output node is substantially equivalent to the rising slew rate and the falling slew rate of the first node.

3 more elements

A controlled slew rate output buffer for providing an input signal to an output node, the input signal having a rising edge and a falling edge, the controlled slew rate output buffer comprising:

input means for generating a charging current in response to the rising edge of the input signal and for generating a discharging current in response to the falling edge of the input signal, the charging current and the discharging current being substantially constant over a temperature range and a power supply voltage range;
intermediate charging means for charging an intermediate node from a first low voltage to a first high voltage at a first slew rate in response to the charging current so that the first slew rate is substantially constant over the temperature range and the power supply voltage range;
intermediate discharging means for discharging the intermediate node from the first high voltage to the first low voltage at a second slew rate in response to the discharging current so that the second slew rate is substantially constant over the temperature range and the power supply voltage range;
output charging means for charging the output node from a second low voltage to a second high voltage at a third slew rate in response to the intermediate node being charged so that the third slew rate is substantially constant over the temperature range, the power supply voltage range, and an output capacitance range and so that the third slew rate is substantially equivalent to the first slew rate;
and
output discharging means for discharging the output node from the second high voltage to the second low voltage at a fourth slew rate in response to the intermediate node being discharged so that the fourth slew rate is substantially constant over the temperature range, the power supply voltage range, and the output capacitance range and so that the fourth slew rate is substantially equivalent to the second slew rate.

3 more elements

Dependencies are inferred from the claim text.