Constant current generation circuit and constant current setting method for the constant current generation circuit

【0001】

[Technical field to which the invention belongs]

The present invention relates to a constant current generation circuit having a small temperature dependence, and more particularly to a constant current generation circuit capable of improving accuracy with respect to a target current value by trimming, and a method for setting a constant current of the constant current generation circuit.

【0002】

[Conventional technology]

The performance required for a constant current generation circuit is that it has high accuracy with respect to the target current value, is not affected by fluctuations in temperature and power supply voltage, and it is also important that all circuits can be easily integrated on one chip. The desired constant current can be created by applying the threshold voltage of a constant current diode or FET, but when trying to obtain a certain level of performance, the output voltage of the constant voltage circuit is converted from voltage to current. It is generally converted into an electric current by a circuit. For example, the difference between the threshold voltages of two transistors is converted into voltage-current by a resistor, and then the current obtained by the conversion is converted into current-voltage by a resistor of the same type. There was a circuit that amplifies the value-voltage difference to obtain a reference voltage (see, for example, Patent Document 1).

【0003】

On the other hand, in recent years, as a constant voltage circuit, a bandgap regulator having a small temperature dependence and suitable for an integrated circuit is often used. For example, by monitoring the forward voltage with a band gap type reference voltage that uses the forward voltage of the resistor and pn junction, the magnification applied to the thermal voltage can be adjusted by trimming the resistor, and the temperature characteristics of the reference voltage can be adjusted. There was a reference voltage circuit to correct (see, for example, Patent Document 2).

【0004】

FIG. 2 is a circuit diagram showing an example of a conventional constant current generation circuit using such a constant voltage circuit and a voltage-current conversion circuit. The constant current generation circuit 100 in FIG. 2 converts the output voltage Vo of the bandgap regulator 101, for example, about 1.25V, into a constant current by the voltage-current conversion circuit 102 and outputs it. The bandgap regulator 101 is known, and its operation description will be omitted here.

【0005】

In the voltage-current conversion circuit 102, the operational amplifier 121 and the NMOS transistor 122 control the voltage across the resistor 123 so that it has the same value as the output voltage Vo of the constant voltage circuit 101. Therefore, a current (Vo / R123) obtained by dividing the output voltage Vo of the constant voltage circuit 101 by the resistance value R123 of the resistor 123 flows through the resistor 123. The current becomes the drain current of the NMOS transistor 122, and is output from the drain of the MOSFET transistor 125 via the MOSFETs 124 and 125 constituting the current mirror circuit.

【0006】

As described above, the output current Io from the voltage-current conversion circuit 102 is determined by the output voltage Vo of the constant voltage circuit 101 and the resistance value of the resistor 123. Therefore, in order to set the constant current Io as the target value, , It can be seen that the output voltage Vo of the constant voltage circuit 101 should be adjusted, or the resistance value of the resistor 123 should be adjusted. However, since the output voltage Vo of the constant voltage circuit 101 is a physically determined value, the resistance value of the resistor 123 is usually trimmed and set.

【0007】

There are two methods for trimming the resistor 123: measuring the output current Io and determining the amount of trimming from the amount of deviation from the target value, and trimming the resistor 123 while measuring the output current Io, and the output current Io is the target. There was so-called function trimming, in which trimming was terminated when the value was reached.

【0008】

[Patent Document 1]

Japanese Unexamined Patent Publication No. 7-44255 [Patent Document 2]

JP-A-2002-91589 [0009]

[Problems to be Solved by the Invention]

However, although the former trimming method described above can be performed in a short time, if the amount of deviation between the output current Io and the target value is large, the trimming accuracy deteriorates. Therefore, when the deviation amount is large, the output current Io can be set to a desired target value by repeating the same trimming twice or three times with the trimming amount slightly reduced in order to improve the accuracy. However, there is a problem that the time required for trimming becomes long.

【0010】

Further, the latter trimming method described above has a problem that the adjustment accuracy of the output current Io is high, but trimming takes time, and a dedicated trimming device is required for function trimming. Further, even if the resistance 123 is trimmed to adjust the resistance value to the optimum value, the resistance value of the resistance 123 changes depending on the temperature, so that there is a problem that the output current Io changes. Further, when the constant voltage circuit 101 and the voltage-current conversion circuit 102 are integrated in the IC, the resistor 123 formed in the integrated circuit usually has a temperature dependence, so that the constant voltage circuit 101 has a band having a small temperature dependence. Even if a gap regulator is used, the output current Io has a temperature dependence, and there is a problem that an accurate constant current output cannot be obtained.

【0011】

The present invention has been made to solve the above problems, and by canceling the change in the constant current output due to the temperature dependence of the resistor built in the integrated circuit, the constant with a small temperature dependence. It is an object of the present invention to obtain a constant current setting method of a current generation circuit and its constant current generation circuit.

【0012】

[Means for solving problems]

The constant current generation circuit according to the present invention includes a constant voltage circuit unit formed by a band gap reference that generates and outputs a predetermined constant voltage from the power supply voltage of a DC power supply, and a constant voltage circuit unit output from the constant voltage circuit unit. In a constant current generation circuit including a voltage-current conversion circuit unit that converts a voltage into a current and outputs a predetermined constant current, the constant voltage circuit unit includes a first arithmetic amplifier that outputs the predetermined constant voltage. , A first resistance circuit in which a combined resistance is generated by a plurality of resistors and the output voltage of the first arithmetic amplifier is input to one end, the other end of the first resistance circuit, and the negative power supply voltage of the DC power supply. The first resistor and the first diode connected in series are connected in series, and the connection portion between the first resistor and the first diode is connected to one input end of the first arithmetic amplifier. A second resistor, a third resistor, and a second diode connected between the series circuit, the other end of the first resistance circuit, and the negative power supply voltage of the DC power supply are connected in series, and the first resistor is connected. A second series circuit in which a connection portion between the second resistor and the third resistor is connected to the other input end of the first arithmetic amplifier is provided, and the voltage-current conversion circuit portion outputs from the constant voltage circuit portion. A current supply circuit that outputs the constant voltage and a current corresponding to the constant voltage, and a combined resistance are generated by a plurality of resistors, and the constant voltage output from the constant voltage circuit unit is generated by the current supply circuit. The second resistor is provided with a second resistance circuit in which a voltage is applied and a current corresponding to the constant voltage is supplied, and an output circuit that outputs a current corresponding to the current flowing through the second resistance circuit. The circuit is composed of the plurality of resistors and a plurality of fuses, and the current corresponding to the constant voltage from the constant voltage circuit unit is the second resistance circuit so that the output current from the output circuit becomes a desired value. Each fuse is selectively cut so as to flow through the combined resistance of the above.

【0013】

Specifically, the first resistance circuit is composed of the plurality of resistors and a plurality of fuses, and each fuse is selectively selected so as to have a temperature characteristic that cancels the temperature characteristic of the voltage-current conversion circuit unit. I tried to be disconnected.

【0014】

Further, the second resistance circuit may include a switch circuit that switches according to a control signal input from the outside and changes the combined resistance of the second resistance circuit.

【0015】

On the other hand, in the current supply circuit, a second operational amplifier in which a constant voltage from the constant voltage circuit unit is input to one input terminal and a control signal input terminal are connected to the output end of the second operational amplifier, and DC It includes a transistor that supplies current from the power supply to the second resistance circuit, and the other input end of the second operational amplifier is connected to the input end of the second resistance circuit to which the current from the transistor is input. I tried to be done.

【0016】

Further, the constant current setting method according to the present invention is composed of a plurality of resistors and a plurality of fuses, and the output voltage changes according to the combined resistance of the first resistance circuit set by selectively cutting the fuses. It is set by having a constant voltage circuit part formed by a band gap reference that generates and outputs a predetermined constant voltage from the power supply voltage of a DC power supply, and having a plurality of resistors and a plurality of fuses, and selectively cutting the fuses. The constant voltage output from the constant voltage circuit unit is converted into a current to output a constant current corresponding to the current flowing through the combined resistance of the second resistance circuit to which the output voltage from the constant voltage circuit unit is applied. A switch provided with a voltage-current conversion circuit unit that outputs a predetermined constant current, and the voltage-current conversion circuit unit switches according to a control signal input from the outside to change the combined resistance of the second resistance circuit. In the constant current setting method of the constant current generation circuit having a circuit, the switch circuit is switched, and the output current of the voltage-current conversion circuit unit is measured for each combined resistance of the second resistance circuit corresponding to the switching. Then, from the output current value of the voltage-current conversion circuit unit measured for each combined resistance value of the second resistance circuit, an approximate calculation is performed to show the relationship between the combined resistance and the output current. Was obtained, and the combined resistance value of the second resistance circuit with respect to the desired output current value was obtained from the obtained characteristics.

【0017】

Further, the temperature characteristic of the combined resistance of the second resistance circuit with respect to the desired output current value is obtained, the combined resistance of the first resistance circuit that cancels the obtained temperature characteristic is obtained, and the obtained combined resistance is used. The fuse of the first resistance circuit is selectively blown so as to be so that the switch circuit is switched, and the output current of the voltage-current conversion circuit unit for each combined resistance of the second resistance circuit corresponding to the switching is set. The relationship between the combined resistance and the output current is shown by performing an approximate calculation from the output current value of the voltage-current conversion circuit unit measured for each of the combined resistance values of the second resistance circuit. The obtained characteristics are obtained, and the combined resistance value of the second resistance circuit with respect to the desired output current value is obtained from the obtained characteristics so that the combined resistance of the second resistance circuit becomes the obtained combined resistance value. The fuse of the second resistance circuit is selectively blown.

【0018】

Specifically, the output current of the voltage-current conversion circuit unit is measured for each of the three types of combined resistance of the second resistance circuit according to the switching of the switch circuit, and the three types of the second resistance circuit are combined. Even if an approximation calculation is performed from the output current value of the voltage-current conversion circuit unit measured for each resistance value to obtain a characteristic forming a quadratic curve showing the relationship between the combined resistance and the output current. Good.

【0019】

BEST MODE FOR CARRYING OUT THE INVENTION

Next, the present invention will be described in detail based on the embodiments shown in the drawings. First Embodiment. FIG. 1 is a circuit diagram showing an example of a constant current generation circuit according to the first embodiment of the present invention. In FIG. 1, the constant current generation circuit 1 includes a constant voltage circuit 2 constituting a bandgap reference and a voltage-current conversion circuit 3 that converts the constant voltage Vo1 output from the constant voltage circuit 2 into a current and outputs the current. It is composed of. The constant voltage circuit 2 forms a constant voltage circuit section, and the voltage-current conversion circuit 3 forms a voltage-current conversion circuit section. The constant voltage circuit 2 and the voltage-current conversion circuit 3 are operated by the power supply supplied from the DC power supply 5, and the current output from the voltage-current conversion circuit 3 becomes the output current Io1 of the constant current generation circuit 1.

【0020】

The constant voltage circuit 2 is composed of an operational amplifier 11, pnp transistors 12, 13, resistors A1 to Am (m is an integer of m> 1), 14 to 16, and fuses FA1 to FAm. The operational amplifier 11 is the first operational amplifier, the resistors A1 to Am and the fuses FA1 to FAm are the first resistance circuit, the pnp transistor 12 and the resistor 14 are the first series circuit, and the pnp transistors 13 and the resistors 15 and 16 are. Each second series circuit is formed. The pnp transistor 12 forms the first diode, and the pnp transistor 13 forms the second diode.

【0021】

A series circuit in which resistors A1 to Am are connected in series and a series circuit in which resistors 14 and pnp transistors 12 are connected in series are connected between the output terminal of the operational amplifier 11 and the negative power supply voltage GND of the DC power supply 5. They are connected in series. The corresponding fuses FA1 to FAm are connected in parallel to the resistors A1 to Am, respectively, and the series circuit of the resistors 15, 16 and the pnp transistor 13 is connected in parallel to the series circuit of the resistors 14 and the pnp transistor 12.

【0022】

The connection b between the resistor 14 and the pnp transistor 12 is connected to the non-inverting input end of the operational amplifier 11, and the connection c between the resistors 15 and 16 is connected to the inverting input terminal of the operational amplifier 11. The connection portion of the resistor Am, the fuse FAm, and the resistors 14 and 15 is referred to as the connection portion a. Also, pnp preparative at transistor 12, base connected to the collector, in the pnp transistor 13, base connected to the collector, and has a respective pnp transistors 12, 13 diode. The voltage output from the output end of the operational amplifier 11 forms the output voltage Vo1 of the constant voltage circuit 2.

【0023】

Next, the voltage-current conversion circuit 3 includes an operational amplifier 21, an NMOS transistor 22 to 24, a MOSFET transistor 25,26, resistors B1 to Bn (n is an integer of n> 1), 27 to 29, and fuses FB1 to FBn. It is composed of. The arithmetic amplifier 21 and the NMOS transistor 24 form a current supply circuit, the MOSFET transistors 25 and 26 form an output circuit, and the NMOS transistors 22, 23, resistors B1 to Bn, and fuses FB1 to FBn form a second resistance circuit, respectively. Transistors 22 and 23 form a switch circuit. The output voltage Vo1 of the constant voltage circuit 2 is input to the non-inverting input terminal of the operational amplifier 21, and the output terminal of the operational amplifier 21 is connected to the gate of the NMOS transistor 24.

【0024】

The facsimile transistors 25 and 26 form a current mirror circuit, each gate is connected and connected to the drain of the MIMO transistor 25, and each source of the MIMO transistors 25 and 26 is the positive power supply voltage of the DC power supply 5, respectively. Vbat is applied. An NMOS transistor 24, resistors B1 to Bn and 27 to 29 are connected in series between the drain of the epitaxial transistor 25 and the negative power supply voltage GND of the DC power supply 5, and the resistors B1 to Bn are supported. The fuses FB1 to FBn are connected in parallel.

【0025】

An NMOS transistor 22 is connected in parallel to a series circuit of a resistor 28 and a resistor 29, and an NMOS transistor 23 is connected in parallel to the resistor 29. An external control signal S1 is input to the gate of the NMOS transistor 22, and an external control signal S2 is input to the gate of the NMOS transistor 23. The current output from the drain of the epitaxial transistor 26 forms the output current Io1.

【0026】

In such a configuration, the voltage-current conversion circuit 3 will be described. Resistors B1 to Bn are resistors for trimming, and fuses FB1 to FBn for trimming are connected in parallel to each resistor. The MIMO transistor 22, which forms a switch circuit, turns on when a high-level signal is input to the gate, connects the connection between the resistor 27 and the resistor 28 to the negative power supply voltage GND, and connects the source and negative side of the IMS transistor 24. The combined resistance value α with the power supply voltage GND can be reduced. Similarly, the MIMO transistor 23 forming the switch circuit is connected between the connection between the resistor 28 and the resistor 29 and the negative power supply voltage GND, and turns on when a high level signal is input to the gate, and the resistor 28 is turned on. The combined resistance value α can be reduced by connecting the intersection of the resistor 29 and the resistor 29 to the negative power supply voltage GND.

【0027】

The operational amplifier 21 and the NMOS transistor 24 control the source voltage of the MOSFET transistor 24 to be the same as the output voltage Vo1 of the constant voltage circuit 2. From this, the current (Vo1 / α) obtained by dividing the output voltage Vo1 of the constant voltage circuit 2 by the combined resistance value α flows through the resistance groups of the resistors B1 to Bn and 27 to 29 of the voltage-current conversion circuit 3. The current becomes the drain current of the MIMO transistor 24, and is output from the drain of the MOSFET transistor 26 via the MOSFET transistors 25 and 26.

【0028】

Here, assuming that each resistance value of resistors B1 to Bn is RB1 to RBn and each resistance value of resistors 27 to 29 is R27 to R29, the combined resistance value α before trimming is (R27 + R28 + R29). Is. Now, the output current Io1 when both the NMOS transistors 22 and 23 are off is as shown in Eq. (1) below. Io1 = Vo1 / (R27 + R28 + R29) .................. (1) [0029]

Next, the output current Io1 when the NMOS transistor 22 is off and the NMOS transistor 23 is on is as shown in Eq. (2) below. Io1 = Vo1 / (R27 + R28) .................. (2) The output current Io1 when the NMOS transistor 22 is turned on is given by the following equation (3). Will be. Io1 = Vo1 / (R27) .................. (3) [0030]

The combined resistance value α at which the target output current Io1 is obtained is approximately calculated from each output current Io1 of the above equations (1) to (3) and the combined resistance value α at that time, and the MIMO transistors 22 and 23 are turned on / off. Determine the combination to be used and the fuses FB1 to FBn to be blown by trimming. In this way, using two NMOS transistors 22 and 23, the output current Io1 for each of the three types of combined resistance value α is measured, and a quadratic curve showing the relationship between the combined resistance value α and the output current Io1 is obtained. Obtainable. Therefore, the non-linear portion of the NMOS transistor 24 can be supplemented, and the combined resistance value α for obtaining the desired output current Io1 can be obtained from the quadratic curve.

【0031】

For example, when the output current Io1 is used in a switching frequency generation circuit of a DC-DC converter, the switching frequency is measured for each on / off combination of the NMOS transistors 22 and 23, and the switching frequency and the combined resistance value α are calculated. By performing an approximate calculation, it is possible to compensate for the non-linearity that occurs in the portion where the switching frequency is generated from the output current Io1. Needless to say, if linear approximation provides sufficient accuracy, delete either one of the NMOS transistors 22 or 23 and use two measurement points for the combined resistance value α and output current Io1 to simplify the approximation calculation. You may.

【0032】

On the other hand, when the voltage-current conversion circuit 3 is integrated in the IC, each of the resistance elements constituting the resistors B1 to Bn and 27 to 29 has temperature dependence, and the output current Io1 is the target by the above method. Even if the fuses FB1 to FBn are trimmed to the current value, they may deviate from the target current value due to temperature changes. When P-type polysilicon resistors are used for resistors RB1 to RBn and 27 to 29, the temperature coefficient is about 600 ppm / ° C. That is, when the P-type polysilicon resistor is used, the output current Io1 fluctuates by 0.6% every time the temperature changes by 1 ° C. For example, when used in a portable device, the temperature change can be as much as 60 ° C or more because it must correspond to a temperature range exceeding 40 ° C from below freezing point. Assuming that the temperature change is 60 ° C, the fluctuation of the output current Io1 is 3.6%, which may deviate from the target current value depending on the application.

【0033】

Therefore, the output voltage Vo1 of the constant voltage circuit 2 input to the voltage-current conversion circuit 3 should have a temperature dependence, and the temperature coefficients of the resistors B1 to Bn and 27 to 29 of the voltage-current conversion circuit 3 should be cancelled. It should be. Here, the output voltage Vo1 of the operational amplifier 11 is derived. Set the base-emitter voltage of the pnp transistor 12 to VBE1 and the base-emitter voltage of the pnp transistor 13 to VBE2, and make the resistance values of the resistors 14 and 15 the same.

【0034】

The connection unit b and the connection unit c in FIG. 1 have the same voltage because they are connected to the two input terminals of the operational amplifier 11. Further, since the resistor 14 and the resistor 15 are commonly connected at the connection portion a, the voltages across the resistor 14 and the resistor 15 are equal. That is, the collector currents Ic of the pnp transistors 12 and 13 are equal to each other, and the collector currents Ic are expressed by the following equation (4).<img file="JP2004192518A_D0001.tif" />In the above equation (4), N is the emitter area ratio of the pnp transistor 12 and the pnp transistor 13, Is is the saturation current of the pnp transistor 12 and the pnp transistor 13, k is the Boltzmann constant, and q is the electron charge. The quantity, T, is the absolute temperature.

【0035】

From the above equation (4), the base-emitter voltage VBE1 and VBE2 can be expressed as the following equations (5) and (6). VBE1 = (k × T) / q × ln (Ic / Is) .................. (5) VBE2 = (k × T) / q × ln {Ic / (N × Is)} .................. (6) [0036]

If the resistance values of the resistors 14 to 16 are R14 to R16, then VBE1 = Ic × R16 + VBE2, so (k × T) / q × ln (Ic / Is) = Ic × R16 + (k × T). ) / Q × ln (Ic / N × Is) .................. (7) When Ic is calculated from the above equation (7), the following equation (8) is obtained. Will be. Ic = (k × T) / q × ln (N) /R16 .................. (8) [0037]

From the above results, assuming that the combined resistance value between the output end of the operational amplifier 11 and the connection portion a is β, the output voltage Vo1 of the operational amplifier 11 is as shown in Eq. (9) below.<img file="JP2004192518A_D0002.tif" /> 【0038】

Resistors A1 to Am and 14 to 16 are made of high-resistance polysilicon and have a temperature coefficient of about -2300 ppm / ° C. Equation (9) is VBG / (1-KT × T). ), The temperature dependence of the voltage-current conversion circuit 3 can be canceled by setting the resistors A1 to Am and 14 to 16. VBG is the voltage corresponding to the energy band gap, and KT is the temperature coefficient of the combined resistance value α.

【0039】

Next, the trimming procedure for each fuse FA1 to FAm of the constant voltage circuit 2 and each fuse FB1 to FBn of the voltage-current conversion circuit 3 will be described. First, before trimming each fuse FB1 to FBn, the MIMO transistors 22 and 23 of the voltage-current conversion circuit 3 are turned on / off alternately, and an approximation calculation is performed to obtain the combined resistance value α and the output current Io1. A quadratic curve showing the relationship with is obtained, and a combined resistance value α with respect to a desired output current Io1 is obtained from the obtained quadratic curve. From the obtained combined resistance value α, select the fuse to be blown from the fuses FB1 to FBn. Among the fuses FA1 to FAm, the fuse to be cut is selected, trimmed and cut so as to cancel the temperature coefficient of the combined resistance value α of the resistance 27 to 29 to which the selected fuse is connected.

【0040】

When the selected fuse of the fuses FA1 to FAm is blown, the output voltage Vo1 of the constant voltage circuit 2 changes slightly, so the MIMO transistors 22 and 23 of the voltage-current conversion circuit 3 are turned on / off alternately. An approximate calculation is performed to obtain a quadratic curve showing the relationship between the combined resistance value α and the output current Io1, and the combined resistance value α with respect to the desired output current Io1 is obtained from the obtained quadratic curve. From the obtained combined resistance value α, a fuse to be cut is selected from the fuses FB1 to FBn, trimmed and cut. In the constant current generation circuit according to the first embodiment, by trimming the fuses FA1 to FAm and FB1 to FBn in this procedure, it is possible to obtain a constant current generation circuit with high accuracy and low temperature dependence. it can.

【0041】

[Effect of the invention]

As is clear from the above description, according to the constant current generation circuit of the present invention, the temperature characteristics of the voltage-current conversion circuit unit can be offset by giving the first resistance circuit of the constant voltage circuit unit the temperature characteristics. Therefore, even if a resistor with a small temperature coefficient cannot be used in the voltage-current conversion circuit section by converting it to an IC, it is possible to generate and output a stable constant current with high accuracy.

【0042】

Further, according to the constant current setting method of the present invention, an approximation calculation is performed from the output current value of the voltage-current conversion circuit unit with respect to each combined resistance value of the second resistance circuit obtained by switching the switch circuit. The characteristics showing the relationship between the combined resistance of the second resistance circuit and the output current were obtained, and the combined resistance value of the second resistance circuit with respect to the desired output current value was obtained from the obtained characteristics. From this, the combined resistance value of the second resistance circuit can be obtained before the desired fuse is trimmed and blown, the fuse to be blown can be selected, and a highly accurate constant current setting can be performed in a short time. It can be carried out.

[Simple explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a constant current generation circuit according to the first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a conventional constant current generation circuit.

[Explanation of symbols]

1 Constant current generation circuit 2 Constant voltage circuit 3 Voltage-current conversion circuit 5 DC power supply 11,21 Operation amplifier 12,13 pnp Transistor 22 ~ 24 NMOS transistor 25,26 NMOS transistor A1 ~ Am, B1 ~ Bn, 14 ~ 16,27 ~ 29 Resistance FA1 ~ FAm, FB1 ~ FBn Hughes