Slew rate adjusting circuit
AssigneeNEC Corporation
InventorKenichi Tanaka
Life of this patent
Estimating the term…
Abstract
An interface circuit includes a slew rate control unit 110, a pre buffer unit 120, and a main buffer unit 130. The slew rate control unit 110 is configured as a current source circuit of the pre buffer unit 120. The slew rate control unit 110 provides a constant current value by using a loop circuit which consists of a slew rate control macro 111, a decoder 112, a comparator 113, N transistor 114, an external terminal resistance (Rref) 115, and a reference voltage (Vref) 116. A size of the N transistor 114 is adjusted based on a code gradually changed in the loop circuit, and finally the current value is determined uniquely.
Claims5
A slew rate adjusting circuit comprising:
- a pre buffer unit which receives an input signal;
- a slew rate control unit which determines a current value of a current supplied to the pre buffer unit and automatically controls a slew rate of the input signal;
- and
- a main buffer unit which receives the input signal from the pre buffer unit and outputs an interface output with a slew rate controlled by the slew rate control unit;
- wherein said slew rate control unit comprises:
- an external terminal resistance;
- a first comparator which compares a voltage dropped by the external terminal resistance with a predetermined reference voltage;
- a slew rate control macro which generates and outputs a slew rate code based on a comparison result of the first comparator;
- and
- a first transistor which changes its own electrical characteristics according to the slew rate code, wherein the slew rate control macro compares the currently generated slew rate code with the previous slew rate code generated immediately before the currently generated slew rate code, and outputs a smaller one of the slew rate codes, and wherein a constant current value is autonomously determined so that the voltage dropped by the external terminal resistance becomes equal to the predetermined reference voltage, by repeating the output operation of the slew rate code and the changing of the electrical characteristics of the first transistor.
A method of adjusting a slew rate comprising the steps of:
- receiving, at a pre buffer unit, an input signal;
- determining a current value of a current provided to the pre buffer unit and automatically controlling a slew rate of the input signal;
- and
- receiving the input signal from the pre buffer unit, and outputting an interface output at the controlled slew rate in response to inputting of the input signal;
- wherein the step of controlling the slew rate comprises the sub steps of:
- comparing a voltage dropped by an external terminal resistance in a circuit with a predetermined reference voltage;
- generating a slew rate code based on a result of the comparing step, and outputting the generated slew rate;
- and
- providing the slew rate to a transistor which is capable of changing its own electrical characteristics according to the slew rate code, wherein the sub step of generating and outputting the slew rate code compares the currently generated slew rate code with the previous slew rate code which is generated immediately before the currently generated slew rate code, and outputs a smaller slew rate code, and a constant current value is determined autonomously so that the voltage dropped by an external terminal resistance becomes equal to the predetermined reference voltage, by repeating the output operation of the slew rate code and the changing of the electrical characteristics of the transistor.
Dependencies are inferred from the claim text.