JP2008263195A - Reference voltage source circuit using field-effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stable reference voltage generating circuit that is free from influence of junction leak at high temperatures. <P>SOLUTION: A reference voltage source circuit comprises a first pair field effect transistor circuit having conductive gates with different polarities, a second pair field effect transistor circuit having gates with the same conductivity and different impurity concentrations, and a compound circuit for composing differences in work functions of the gate electrodes of the first and second pair field effect transistors at an arbitrary ratio. Only to the field effect transistors M1 to M5 in the composing circuit, a substrate electrode W is separated from a source and is connected to a GND instead. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reference voltage source circuit using a field effect transistor that operates stably even at a high temperature.

  Conventionally, as a voltage generation circuit and a reference voltage source circuit using a field effect transistor (hereinafter simply referred to as a transistor), there is JP-A-2001-284464 shown in FIG. , M2), and the work function difference between the gate materials of the paired transistors (M3, M4) having the same polarity conductivity type and high concentration and low concentration gates are used to obtain the reference voltage.

  In FIG. 1, a transistor M1 has a high-concentration n-type gate (impurity concentration) and connects the gate and source to form a constant current source. The transistor M2 has a high-concentration p-type gate, and a gate potential is applied by a source follower circuit including an n-type channel transistor M5 and a resistor R. The transistor M3 has a high concentration n-type gate. The transistor M4 has a low-concentration n-type gate, and connects the gate to the source to become a constant current source.

  In all the transistors M1, M2, M3, M4, and M5, in particular, the transistors M1 and M2 and the transistors M3 and M4 function as a pair of transistors. The substrate potential is set to the source potential by connecting the substrate electrode W to the source.

  In the first pair transistor, since the same current flows in both transistors M1 and M2, the output voltage V1 is a voltage Vpn having a negative temperature coefficient, and the second pair transistor is the same as both transistors M3 and M4. Therefore, a voltage −Vptat having a positive temperature coefficient is obtained as the output voltage Vgs between the gate and the source Vgs. The voltage V2 obtained by dividing the voltage V1 (= Vpn) by resistors R1 and R2 and Vgs (= −Vptat) are added to obtain an output voltage V3 from the circuit.

  If the voltage division ratio is set so that the negative and positive temperature coefficients in the voltage Vpn and the voltage Vptat are offset, a reference voltage Vref having no temperature coefficient can be obtained as the output voltage V3.

  In the conventional reference voltage source circuit shown in FIG. 1, when the reverse leakage of the pn junction occurs at a high temperature, the drain-substrate current of the transistor increases, so that the current increases at each stage of the circuit. . Since the first stage composed of the transistors M1 and M2 is composed of a pair transistor, the same current flows through the drain-substrate current of the transistor M1 and the drain-substrate current of the transistor M2. For this reason, Vpn takes the same value as when there is no pn junction leak, and thus is constant without being affected by temperature. The same applies to the third stage including the transistors M3 and M4.

  However, since the transistor M5 constituting the second-stage source follower circuit is not a pair-structured transistor, and the substrate potential is made equal to the source potential, the following problems are caused by the increase in the substrate current of the transistor M5. Occurs.

  FIG. 2 is a graph showing the characteristics of the gate voltage (Vg) / source current (Is) of the transistor, and “1” indicates the characteristics at room temperature. When the drain-substrate current of the transistor increases due to junction leakage at a high temperature, the substrate potential of the transistor M5 is made equal to the source potential as shown in FIG. 1 (the substrate terminal W and the source are in wells independent for each transistor). Therefore, the substrate-source current is added to increase the source current. Therefore, the characteristics indicated by “2” are obtained at high temperatures.

  Since the transistor M5 needs to maintain a constant current Vpn / (R1 + R2) determined by the resistors R1, R2 and Vpn, the gate-source voltage of the transistor M5 decreases from Vg1 to Vg2. The drain voltage of the transistor M2 is given by the gate voltage of the transistor M5 and decreases as the gate-source voltage Vgs decreases. As a result, the drain-source voltage of the transistor M2 also decreases.

  When the drain-source voltage of the transistor M2 becomes (Vth−Vgs) or less, the transistor operation shifts from the saturation region to the linear region, and the transistor M2 passes the current value determined by the transistor M1 serving as the first-stage constant current source. Therefore, it is necessary to increase the Vgs of the transistor M2. As a result, Vgs (Vpn) of the transistor M2 rises and Vref also rises.

  An object of the present invention is to solve the above-described problems. By separating the substrate potential of transistors other than a pair of transistors (transistors constituting a source follower circuit) from the source and connecting them to GND, the junction can be obtained even at high temperatures. To provide a reference voltage source circuit using a field effect transistor capable of obtaining a stable reference voltage independent of leakage.

  The reference voltage source circuit includes a “first pair field effect transistor circuit” having gates having different conductivity types and a “second pair field effect transistor circuit” having gates having the same conductivity type and different impurity concentrations. In order to synthesize the work function difference between the gate electrodes of the first and second pair field effect transistors at an arbitrary ratio, a “synthesis circuit” including a field effect transistor and a resistor is included. As described above, the gate electrode W of each field transistor is connected to the source. However, in the present invention, the substrate electrode W is separated from the source only for the field effect transistor in the “synthesis circuit”. Connected to GND.

  When reverse leakage of the pn junction occurs at a high temperature, the drain-substrate current of the transistor increases, so that the current increases in each stage of FIG. 3 showing the embodiment of the present invention. However, the first stage composed of the transistors M1 and M2 is composed of a pair transistor in which the substrate potential is equal to the source potential (the substrate terminal and the source terminal are in an independent well). The same current flows in the drain-substrate current of M1 and the drain-substrate current of the transistor M2. Therefore, in the process of obtaining Vpn, the influence of the leakage current in both transistors is canceled out, so that Vpn becomes a constant value without being affected by temperature. The same applies to the third stage including the transistors M3 and M4. (This operation is the same as the conventional example)

  Next, the second stage is a source follower circuit constituted by a transistor M5 “a substrate electrode is separated from a source and connected to GND”, which is a feature of the present invention. First, the graph of FIG. 4 shows changes in the drain current (Id), the source current (Is), and the substrate current (Ib) with respect to the temperature of the transistor M5 configured as described above.

  As can be seen from FIG. 4, when the temperature exceeds a certain temperature, the substrate current of the transistor rises due to reverse leakage of the pn junction, and the drain current is the sum of the source current and the substrate current. It increases together. However, since the substrate and the source are independent, the source current is not affected by the increase in the substrate current even at a high temperature.

  As described above, the transistor M5 constituting the source follower circuit needs to maintain a constant current Vpn / (R1 + R2) determined by the resistors R1, R2 and Vpn. The current flowing through the resistors R1 and R2 is equal to the source current of the transistor M5, and the source current is not affected by the leak current (drain-substrate current) by flowing the substrate current to GND as described above. Therefore, in the present invention, a reference voltage source circuit that is stable even at a high temperature can be realized by separating the substrate potential of the source follower circuit transistor from the source potential to GND and using a pair of transistors. Hereinafter, embodiments of the present invention will be described in more detail.

  In FIG. 3, transistors M1, M2, M3, M4, and M5 are all n-channel, and the impurity concentrations of the substrate and channel dove are the same, and are formed in independent p-wells of the n-type substrate, and transistors M1, M2, M3, The substrate potential of M4 is equal to the source potential.

  However, the substrate potential of the transistor M5 constituting the source follower circuit is set to GND independently of the source potential. The ratio (W / L) of the channel width W to the channel length L is equal for the transistors M1 and M2, and is equal for the transistors M3 and M4. The transistor M1 has a high-concentration n-type gate, and the gate is a constant current source in which the source is connected. The transistor M2 has a high-concentration p-type gate, and a gate potential is applied by a source follower circuit including an n-type channel transistor M5 and a resistor R.

  The transistor M3 has a high concentration n-type gate. The transistor M4 has a low-concentration n-type gate, and connects the gate and the source to become a constant current source. Since the same current flows through the pair transistors M1 and M2, the gate-source voltage of the transistor M2 becomes the difference Vpn between the Vth of the transistors M1 and M2.

  Also, since the same current flows through the second pair of transistors M3 and M4, the gate-source voltage difference of the transistors M3 and M4 is 0 because the gate-source voltage of the transistor M4 is 0. This is equal to the source-to-source voltage Vgs, which is a voltage (−Vptat) having a positive temperature coefficient.

If the source potential of the transistor M3 is V3,
From the relationship of V2 = V3 + Vgs, V2 = V1 * R2 / (R1 + R2) V3 = V2 + Vptat = V1 * R2 / (R1 + R2) + Vptat
= Vpn * R2 / (R1 + R2) + Vptat
As described above, the reference voltage Vref having no temperature characteristic can be obtained for V3 by appropriately setting the voltage dividing ratio or changing the impurity concentration of the gate (Vpn and Vgs are changed). it can.

  According to the present invention, it is possible to realize a reference voltage generation circuit using a field effect transistor that is stable even at a high temperature. Specifically, in the invention according to claim 1, by removing the substrate potential of the field effect transistor other than the pair field effect transistor from the source and setting it to GND, the influence of the junction leakage is eliminated, and stable reference voltage generation is possible even at a high temperature. A circuit can be realized.

Diagram of conventional reference voltage source circuit Characteristic diagram showing the relationship between the gate voltage and source current of a transistor The circuit diagram which becomes one Embodiment of this invention Characteristics diagram of drain current, source current and substrate current against temperature change of the transistor used in the present invention

Explanation of symbols

  M1, M2, M3, M4, M5 Field effect transistor, R resistance

Claims (1)

A first pair field effect transistor circuit having gates having different conductivity types, a second pair field effect transistor circuit having gates having the same conductivity type and different impurity concentrations, and first and second pair field In order to synthesize the work function difference of the gate electrode of the effect transistor at an arbitrary ratio, in a reference voltage source circuit composed of a synthesis circuit composed of a field effect transistor and a resistor,
A reference voltage source circuit, wherein a substrate electrode of a field effect transistor in the synthesis circuit is separated from a source and connected to GND.

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