Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Patent
1989-09-05
1991-06-25
Wong, Peter S.
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
323316, G05F 320
Patent
active
050270540
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to voltage sources and particularly to circuits which provide specific voltages which are dependent on the threshold voltage of transistors used in the circuit.
Such circuits are particularly useful in the field of CMOS IC's where it is advantageous to provide specific voltages whose values are proportional to the threshold voltage V.sub.T of the transistors used therein. Such transistors may be either n- or p-channel field-effect transistors. One application is in logic circuits where threshold voltage dependent voltages are required in order to switch the transistors in the circuit so that logical decisions are made by the circuit. Another application is in sensing amplifiers in which lines connected to the inputs of the amplifier are precharged by voltages proportional to the threshold voltage in order to improve the sensitivity of the amplifier.
SUMMARY OF THE INVENTION
Therefore it is an object of the invention to provide a circuit which generates voltages whose values are proportional to the threshold voltage of the transistors used in the circuit.
Accordingly, the invention provides a voltage source circuit comprising a current mirror having an input and an output and coupled to a first reference potential line;
a reference current source coupled to the current mirror input or generating a reference current which is proportional to a threshold voltage; and
a bias transistor having a first current electrode coupled to the current mirror output, a second current electrode coupled to a second reference potential line and a control electrode coupled so as to produce at its first current electrode a voltage dependent on the reference current,
wherein said current mirror output forms an output of the voltage source circuit.
Preferably the reference current source comprises a transistor having a first current electrode coupled to said current mirror input, a second current electrode coupled to said second reference potential line and a control electrode for receiving on input reference voltage.
As will be more fully described below, the control electrode of the bias transistor may be coupled to received either the input reference voltage or the voltage level at the current mirror output, depending on the required output from the voltage source circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be more fully described by way of example with reference to the drawings of which:
FIGS. 1A and 1B show circuit diagrams of a basic embodiment of a voltage source circuit according to the invention; and
FIGS. 2A and 2B show circuit diagrams of an improved embodiment of a voltage source circuit according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
Thus, FIGS. 1A and 1B show circuit diagrams of a voltage source circuit providing voltages which are dependent on the threshold voltage of n-channel transistors. It comprises a current mirror composed of p-channel transistors M.sub.2 and M.sub.3 each having one current electrode coupled to a voltage supply line V.sub.DD. Transistor M.sub.2 is diode-coupled with its second current electrode coupled to its gate electrode which is also coupled to the gate electrode of transistor M.sub.3. The input to the current mirror comprises the second current electrode of transistor M.sub.2 which is coupled to the first current electrode of an n-channel transistor M.sub.1. This transistor has its second current electrode coupled to a ground reference potential line and its gate electrode coupled to receive an input reference voltage V.sub.REF.
In this embodiment of the voltage source circuit, the input reference voltage V.sub.REF is arranged to be twice the threshold V.sub.T of the n-channel transistors. Thus: and biased by a voltage V is described by is the mirror through transistor M.sub.3 is: M.sub.2 and M.sub.3.
The output of the current mirror is coupled to the drain of an n-channel bias transistor M.sub.4, this drain forming the output of the voltage source circuit. The source of transistor M.sub.
REFERENCES:
patent: 4588941 (1986-05-01), Kerth et al.
patent: 4638239 (1987-01-01), Hachimori
patent: 4675593 (1987-06-01), Minakuchi
patent: 4713600 (1987-12-01), Tsugaru et al.
patent: 4751463 (1988-06-01), Higgs et al.
Bingham Michael D.
Botsch Bradley J.
Motorola Inc.
Wong Peter S.
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