VARIABLE TEMPERATURE COEFFICIENT LEVEL SHIFTER

Abstract: A variable temperature coefficient level shifter includes a circuit which generates a voltage V<uBE>u having a negative temperature coefficient and a voltage //c V<uBE>u having a positive temperature coefficient. A control current is generated by placing a first resistor (R<uN>u) between V<uBE>u and ground and a second resistor (R<up>u) between //c V<uBE>u and ground. Each of these currents forms a component of the control current which then has some net temperature coefficient. By properly scaling the resistors the control current may have any desired temperature coefficient between 2800ppm and 3000ppm. Once the temperature coefficient is set, a third resistor (R<uS>u) is provided through which the control current flows. The amplitude of the shift is then selected by selecting the value of resistor (R<uS>us).

Description: VARIABLE TEMPERATURE COEFFICIENT LEVEL SHIFTER Background of the Invention Field of the Invention: This invention relates generally to a voltage level shifter and, more particularly, to a circuit for generating a voltage having an independently controllable temperature coefficient and amplitude. Description of the Prior Art: The need often arises to provide an output current or voltage having a zero temperature coefficient, and circuits for accomplishing this are well-known. For example, refer¬ ence is made to U.S. Patent 3,887,863 entitled "Solid-State Regulated Voltage Supply", U.S. Patent 3,617,859 entitled "Electrical Regulator Apparatus Including A Zero Temperature Coefficient Voltage Reference Circuit", and U.S. Patent 3,893,018 entitled "Compensated Electronic Voltage Source". Such circuits generally offset the negative temperature coefficient of a base-to-emitter voltage (V BE ) of one transistor with a positive temperature coefficient derived from the base-tσ-emitter voltage differential (ΔV BE ) between a pair of transistors. One of the problems associated with this prior art technique is that the amount of negative temperature coefficient that may be introduced into the output is severely restricted by a single V Br . Summary of the Invention It is an object of the present invention to provide a voltage level shifting circuit having a controllable temperature coefficient and which produces a stable independently controllable level sh . ifting voltage a p! itude. -^ j _r It is a further object of the present invention to provide a voltage level shifting circuit having a controllable temperature coefficient and an independently controllabl shift amplitude which is not affected by circuitry coupled to its output or otherwise associated therewith- It is still further object of the invention to provide a voltage level shifting circuit having a controllable temperature coefficient and an ndependently controllable shift amplitude which does not require multiplying or the use of resistive voltage dividers. According to a first aspect of the invention there is provided a level shifting circuit for producing an output voltage having a desired amplitude and temperature coefficient s comprisi πg: a first supply voltage terminal ; a second supply voltage terminal ; a first current source coupled to said first supply voltage terminal for generating a first current having a positive temperature coefficients a second current source coupled to said first supply voltage terminal for generating a second current having a negative temperature coefficient; and first resist! ve means coupled between said first and second current sources and said second supply voltage terminal for combining, said first and second currents to produce a third current having a net temperature coefficient correspond ng to said desired temperature coefficient and for generating from said third current a voltage having said net temperature coefficient, said voltage having said desired amp! itude- According to a further aspect of the invention there is provided a method for level shifting a voltage, the amplitude of the level shift and the temperature coefficient thereof being independently controllable, comprising: generating a first current having a positive temperature coefficient; generating a second current having a negative temperature coefficient; varying the magnitude OMPI of said first and second currents to achieve a net negative, zero, or positive temperature coefficient; and applying the sum of said first and second currents to a first resistive means the resistance of which being chosen to produce a required level shift. Brief Description of the Drawings The above and other objects, features and advantages of the present invention will be more clearly understood i from the following detailed description taken in conjunction with the accompanying drawing in which the sole figure is a diagram, partially in block form and partially in schematic form, illustrating the invention. Description of the Preferred Embodiment The inventive arrangement shown in the drawing includes first and second resistors R^ and Rp coupled between ground and nodes 4 and 6 respectively. A third resistor R$ is coupled to a source of supply voltage (V+) and to- node 2 from which the circuit output is taken. Block 8 which is coupled to nodes 2, 4, and 6 as shown includes circuitry for generating a first voltage V £ and a second voltage ΔV BE , V BE corresponding to the base-emitter voltage of a transistor and having a negative temperature coefficient, and ΔV BE being the base-to- emitter voltage differential between a pair of transistor and having a positive temperature coefficient. Circuits for generating these voltages are well-known and a further description is not deemed necessary here. However, the interested reader is referred to the above-cited U.S. Patent 3,887,863. Resistors R N , R p and R s may be internal to an integrated circuit chip or external thereto. Oϊ.fPI y,\ With V B rr appearing at node 4, the current flowing through R^ has a negative temperature coefficient and a value of VBE/R^. In like manner, with ΔV B £ appearing at node 6, the current flowing through Rp has a positive temperature coefficient associated therewith and a value of ΔV B rr/Rp. Thus, the total current flowing through resistor R$ (IcNT equals V BE /R^ plus ΔV B £/Rp). This current has a net temperature coefficient associated with it which is controlled by properly selecting resistors Rpj and Rp. For example, if RN is open (infiijite impedance), the temperature coefficient of IQNT is totally due to the ΔV B £ component and is therefore positive. If, on the other hand, Rp is open, the temperature coefficient of IQNT ^ s due t0 tπe ^BE term and i s therefore negative. Thus, by properly scaling R N and Rp, the temperature coefficient of I κτ m *Y be varied from approximately -2800 parts-per-mi11 ion to +3000 parts-per- ill on. Now that the temperature coefficient has been set to some desired value, the magnitude of the level shift appearing at node 2 can be set to some desired magnitude by properly selecting resistor R$. The voltage drop across R5 will now have the same temperature coefficient associated therewith as was imparted to the control current *CNT* Thus, a voltage source has been created which has a controllable temperature coefficient and an ndependently controlled magnitude. That is, temperature coefficient is controlled by selecting R^ and Rp, and the magnitude of the shift is controlled by selecting R S . Several advantages of the arrangement shown in the drawing should be noted. First, it is only the ratio of the resistors which sets the amplitude of the level shift and not the absolute values of the resistors. This reduces resistor tolerance requirements as long as the resistors are created using common resistor processing. For example, if the values of R^ and Rp are high, the current will be low. However, since the value of $ will also be high, the resulting level shift remains the same. Second, the level shift voltage across resistor R$ is constant regardless of fluctuations in the supply voltage V+. The above description is given by way of example only. Changes in form and details may be made by one skilled in the art without departing from the scope of the invention.

Claims: (received by the International Bureau on 16 May 1982 (26.05.82)) 1. A level shifting circuit for producing an output voltage having a desired amplitude and temperature coefficient, comprising: a first supply voltage terminal ; a second supply voltage terminal ; a first current source coupled to said first supply voltage terminal for generating a first current having a positive temperature coefficient a second current source coupled to said first supply voltage terminal for generating a second current having a negative temperature coefficient; and first resistive means coupled between said first and second current sources and said second supply voltage terminal for combining said first and second currents to produce a third current having a net temperature coefficient corresponding to said desired temperature coefficient and for generating from said third current a voltage having said net temperature coefficient, said voltage having said desired amplitude. 2. A circuit according to claim 1 wherein said first current source comprises: first means for generating a first voltage having a positive temperature coefficient; 'and second resistive means coupled between said first means and said first supply voltage terminal. ' 3. A circuit according to claim 2 wherein said second current source comprises: second means for generating a voltage having a negative temperature coefficient; and third resistive means coupled between said second means and said first supply voltage terminal. 4. A circuit according to claim 3 wherein said second current corresponds to the base emitter voltage of a transistor and wherein said first current corresponds to the base-emitter voltage differential of a pair of transistors. 5 (Amended) . A level shif ing circuit for coupling to a first source of a first yoltage having a positive temperature coefficient and to a second source of a second voltage having a negative temperature coefficient for the purpose of producing a voltage having a desired temperature coefficient and amplitude, comprising: a first supply voltage terminal; a second supply voltage terminal; first resistive means coupled between said first supply voltage terminal and said first source for generating a first current having a positive temperature coefficient; second resistive means coupled between said first supply voltage terminal and said second source for generating a second current having a negative temperature coefficient; and third resistive means coupled between said second supply voltage terminal and said first and second sources for combining said first and second currents to produce a third current having a net temperature coefficient and for generating therefrom a voltage having a desired amplitude and temperature coefficient. 6. A method for providing controllable voltage level shift having an independently controllable temperature coefficient, comprising: generating a first voltage having a positive temperature coefficient; generating a second voltage having a negative temperature coefficient; applying said first and second voltages across first and second resistive means the values of which are chosen to result in a current having a desired net temperature coefficient; and applying said total current to a third resistive means the resistance of which determines said voltage level shift. 7. A method according to claim 6 further including: varying said first and second resistive means to varying said net temperature coefficient; and varying said third resistive means to alter said level shift * 8. A method according to claim 7 wherein said net temperature coefficient may be varied from approximately -2800 parts per million to approximately +3000 parts per mi 11 ion. 9. A method for level shifting a voltage, the amplitude of the level shift and the temperature coefficient thereof being independently controllable, comprising: generating a first current having a positive temperature coefficient; • generating a second current having a negative temperature coefficient; varying the magnitude of said first and second currents to achieve a net negative, zero, or positive temperature coefficient; and applying the sum of said first and second currents to a first resistive means the resistance of which being chosen to produce a required level shift.

Inventors: BYNUM BYRON G, GRAY RANDALL C, JARRETT ROBERT B
Applicants: MOTOROLA INC
Application year: 1982
Main classification: G05F3
IPC codes: G05F3