JP2009104452A - Constant current circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure starting of a band gap reference (BGR), without use of a control signal supplied from outside, and without relying on rise characteristics of a power supply voltage. <P>SOLUTION: A constant current circuit includes: a first circuit 101 including a first resistance device R101-1, and a first diode D101-2; a second circuit 102 including a second resistance device R102-1, a second diode D102-2, and a third resistance device R102-3 connected in series with the second diode D102-2; a voltage current converter 103 supplying the first circuit 101 with a first current, supplying the second circuit 102 with a second current, and outputting a third current; and a starting circuit 104 on/off-controlling a starting current according to the third current and supplying the voltage current converter 103 with the starting current. The voltage current converter 103 is connected so as to convert a potential difference between the first circuit 101 and the second circuit 102 into a current, and increases the first current, the second current and the third current according to the starting current. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a constant current circuit, and more particularly to a constant current circuit classified as a band gap reference (BGR) including a startup circuit.

  A general band gap reference (hereinafter referred to as “BGR”) is based on the principle that a voltage proportional to absolute temperature can be obtained when the current per emitter area flowing through two sets of diodes is compared. A current proportional to the temperature is passed through a series circuit consisting of a resistor and a diode, and the voltage drop of the positive temperature coefficient due to the resistor and the voltage drop of the negative temperature coefficient due to the diode are added, so that a temperature coefficient of almost zero is obtained. The voltage is obtained.

  Patent Document 1 discloses a technique for obtaining a current having a temperature coefficient of approximately zero by adding a current flowing through a resistor connected in parallel with a diode while obtaining a current having a positive temperature coefficient using the above principle. is doing. However, since the voltage drop due to the diode has a negative temperature coefficient, the current flowing through the resistor connected in parallel with the diode also has a negative temperature coefficient. The technique of Patent Document 1 is a useful technique that operates even when the power supply voltage is low (for example, 1 V or less).

  A general BGR requires an activation circuit that guarantees the activation of the BGR. In order to operate the activation circuit without using an externally supplied control signal, a function for detecting whether or not the BGR is operating within the normal operation range is necessary. In general BGR, for example, a voltage drop due to a resistor connected in series with a diode is observed, and it is detected that the BGR is operating within a normal operating range according to the observation result.

  However, in Patent Document 1, there is a resistor connected in series with a diode, but the voltage drop due to this resistor is as small as 100 mV or less, and the potentials at both terminals are not fixed. Therefore, Patent Document 1 has a problem that it is difficult to detect whether or not the BGR is operating within a normal operating range by observing a voltage drop caused by a resistor connected in series with a diode.

  For the problem that the voltage drop due to the resistor is small, an estimated value is calculated using a current mirror circuit for the total current value of the current flowing in the diode and the current flowing in the resistor connected in parallel with the diode. A solution to obtain is conceivable.

  However, in order to determine whether or not it is operating normally, a highly accurate threshold value is set, for example, more than half of the current during normal operation and less than the current during normal operation. There is a problem that it is necessary and difficult to realize.

  A technique for generating a starting current using a timer composed of a capacitor and a resistor is known.

  However, in order to use the timer, it is a condition that the maximum time of rising of the power supply voltage is guaranteed to be a certain value or less, and if this condition is not satisfied, whether the power supply voltage has reached the rated power supply voltage or not. It is necessary to use a combination of a detection circuit and a timer, and there is a problem that it is difficult to realize.

That is, the conventional constant current circuit has a problem that it is not possible to guarantee the start of the BGR without using a control signal supplied from the outside and when the rising time of the power supply voltage is not less than a certain value.
Japanese Patent Laid-Open No. 11-45125

  An object of the present invention is to guarantee the start-up of the band gap reference (BGR) without using a control signal supplied from the outside and without depending on the rising characteristic of the power supply voltage.

  According to a first aspect of the present invention, a first circuit including a first resistance element and a first diode, a second resistance element, a second diode, and a third resistance element connected in series with the second diode are included. A second current circuit; a voltage-current converter that supplies a first current to the first circuit; a second current to the second circuit; and outputs a third current; and an on-state activation current according to the third current. A start-up circuit that controls / off and supplies the voltage / current converter to the voltage / current converter, and the voltage / current converter is connected to convert a potential difference between the first circuit and the second circuit into a current. The voltage-current converter increases the first current to the third current according to the start-up current, and a product of an element value of the first resistance element and the first current is an element of the second resistance element A constant current greater than the product of the value and the second current The road is provided.

  According to the present invention, it is possible to guarantee the start of the band gap reference (BGR) without using a control signal supplied from the outside and without depending on the rising characteristic of the power supply voltage.

  Embodiments of the present invention will be described below with reference to the drawings. The following examples are one embodiment of the present invention and do not limit the scope of the present invention.

  First, Example 1 of the present invention will be described.

  1 is a circuit diagram showing a circuit configuration of a constant current circuit according to a first embodiment of the present invention.

  The constant current circuit according to the first embodiment of the present invention includes a first circuit 101, a second circuit 102, a voltage / current converter 103, and a starting circuit 104.

  The first circuit 101 includes a first resistance element R101-1 and a first diode D101-2. The first circuit 101 is a parallel circuit of a first resistance element R101-1 and a first diode D101-2.

  The second circuit 102 includes a second resistance element R102-1, a second diode D102-2, and a third resistance element R102-3. The second circuit 102 is a parallel circuit of a series circuit of the third resistance element R102-3 and the second diode D102-2 and the second resistance element R102-1.

The voltage / current converter 103 is connected to convert a potential difference between the first circuit 101 and the second circuit 102 into a current. The voltage / current converter 103 supplies the first current I ₁ to the first circuit 101, the second current I ₂ to the second circuit 102, and the third current I ₃ to the activation circuit 104.

Since the first current I ₁ , the second current I ₂ and the third current I ₃ are generated by the current mirror, the third current I ₃ is substantially proportional to the first and second currents I ₁ and I ₂ . The voltage-current converter 103 increases the _{first to} third currents I _{1 to} I ₃ when the starting current I ₄ is a positive value.

Here, the product of the element value R ₁ and the first current I ₁ of the first resistance element R 101-1 and the product of the element value R ₂ and the second current I ₂ of the second resistance element R 102-1 are expressed by the relationship of Equation 1. Meet. For example, k = 1.05. That is, while k = 1 in the prior art, k> 1 in the first embodiment of the present invention.

The activation circuit 104 includes MOS transistors M104-1 and 104-2 and a bias circuit 104-3 that applies a bias voltage to the MOS transistors M104-1 and 104-2. Starting circuit 104, the output when the value of the third current _{I 3} is zero, the current _{I th} according to the bias voltage applied to approximately MOS transistor M104-1, as the starting current _{I 4} through MOS transistors M104-2 To do. MOS to a connection point between the transistors M104-1 and MOS transistor M104-2 is supplied third current _{I 3} is supplied from the voltage current conversion section 103, the starting circuit 104, a third supplied from the voltage current conversion section 103 outputs an activation current _{I 4} in accordance with the magnitude relationship between the current _{I 3} and the threshold current _{I th.} The starting current _{I 4} of the third when the current _{I 3} is equal to or lower than a threshold current _{I th} about _I th -I ₃ becomes, in such conditions the third current _{I 3} is the threshold current _{I th} or more, the startup current _{I 4} is Turned off.

Two MOS transistors M104-1,104-2 operates as a current switch for the current control to switch the starting current _{I 4} of the on / off according to the third current _{I 3.} The threshold current I _th is set so that the absolute values of the input voltages V _A and V _B and the input signal V _B −V _A at which the error amplifier 103-2 of the voltage-current converter 103 operates normally become sufficiently large. .

Bias circuit 104-1 is designed according to the starting current _{I 4.} A third current I ₃ ratio of the first current I ₁ or the second current I ₂ is set to the minimum value which can guarantee off the starting current I _4.

  FIG. 2 is a circuit configuration diagram showing a circuit configuration of the voltage / current converter 103.

  The voltage / current converter 103 includes a voltage / current converter 103-1 and an error amplifier 103-2.

The voltage-current conversion circuit 103-1 has a first current I ₁ , a second current I ₂ , a third current from the drains of a plurality of MOS transistors in which the source electrodes are connected in parallel and the gate electrodes are connected in parallel. and it outputs an output current I _out of the constant current circuit according to embodiment 1 of the current I ₃ and the present invention.

The input voltage V _A and the input voltage V _B are input to the error amplifier 103-2, and the voltage / current conversion circuit 103-1 is controlled so that the absolute value of the input signal V _B −V _A becomes small. Further, the starting current I ₄ is input to the error amplifier 103-2, and the output of the error amplifier 103-2 changes according to the starting current I ₄ . Starting current I ₄ is when the positive value, the output of the error amplifier 103-2 to increase the output current of the voltage-current conversion circuit 103-1 is changed.

With the above configuration, when the first and second currents I ₁ and I ₂ are so small that the error amplifier 103-2 cannot correctly determine the polarity of the input signal and control the voltage-current conversion circuit 103-1, The start-up current I ₄ is supplied to the voltage-current conversion circuit 103-1, the first and second currents I ₁ and I ₂ are increased, and the error amplifier 103-2 correctly determines the input signal and the voltage-current conversion circuit 103 -1 can be controlled. Moreover, the starting circuit 104, when the first and second currents I _1, I ₂ becomes the rated current, starting current turned off so that the I _4, the output current I of the constant current circuit according to a first embodiment of the present invention _OUT is not affected by the starting current I ₄ . Therefore, it is possible to guarantee activation of the band gap reference (BGR).

Here, when the _{I 1 × R 1 = k ×} I 2 × R 2 (k> 1) as in Example 1 of the present _{invention, I 1 × R 1 = I} 2 × as in the prior art There is a concern that the temperature characteristics are significantly different from the case of R ₂ (k = 1).

  FIG. 3 is a graph showing temperature characteristics according to Example 1 of the present invention and the related art.

As shown in FIG. 3, when k in Equation 1 is set to k = 1.05, the difference in temperature characteristics is smaller than the current fluctuation amount due to the original temperature characteristics. When k is increased, the allowable threshold range of the activation circuit 104 is widened, but the fluctuation range of the output current I _OUT is widened at the expense of temperature characteristics.

  Next, the effect of setting k> 1 in Equation 1 in Example 1 of the present invention will be described.

4 shows the first and second currents I ₁ and I ₂ of the voltage-current conversion circuit 103-1 and the input voltage V _A of the error amplifier 103-2 when k in Equation 1 is k = 1.05. a graph showing an example for each temperature relationship V _B, k = 1 and then first and second currents as compared with the case were I ₁ as in the prior _art, the input signal when I ₂ is smaller V _B - The absolute value of _VA is large.

Figure 5 is a graph showing a comparison of Example 1 and the prior art of the present invention will function system of the first and second currents _I 1, _{I 2} and the input signal _V B -V _A of the error amplifier 103-2.

The voltage-current converter 103, the input signal _V B -V when _A is negative increases the first through third current _I 1 ~I _3, positive if the first to third current _{I 1} reduce the ~I _3.

As shown in FIG. 5, in Example 1 of the present invention, the first and second currents I ₁ and I ₂ are rated currents (currents at which V _B −V _A becomes zero) of 4 μA of 4 minutes. 1 or less (e.g., 0.5 .mu.A or less) of even a small current value, such as, at about the input signal _V B -V _a voltage-current converter 103 -10 mV, and its absolute value is as large as approximately 10 mV.

In contrast, in the prior art, the first and second currents _I 1, if _{I 2} is 0.5 .mu.A, the input signal _V B -V _A voltage-current conversion section 103 is about 0 mV, voltage-current conversion The first and second currents I ₁ and I _{2 at which} the input signal of the unit 103 is −10 mV or less (10 mV or more in absolute value) are about 1.4 μA, which is more than half of the rated current 2.4 μA.

For example, if there is an offset voltage of 10mV absolute value to the error amplifier, the input signal _V B -V _A to equilibrate at -10 mV (i.e., to maintain the output current _{I OUT)} so that the error amplifier 103-2 When operating, there are the following differences between the prior art and the first embodiment of the present invention.

In the prior art, when the first and second currents I ₁ and I ₂ are 0.5 μA, the input of the error amplifier 103-2 is about 0 mV, and the first and second currents are offset due to the offset voltage of the error amplifier 103-2. The voltage-current converter 103 is controlled so as to decrease the currents I ₁ and I _2, and the _first and _second currents I ₁ and I ₂ remain zero, and the constant current circuit does not start. In order to guarantee the start-up, the start-up current I ₄ is supplied to the voltage-current converter 103 so that the first and second currents I ₁ and I ₂ are 1.4 μA or more, and the first and second currents I ₁ , _{I 2} must stop the starting current _{I 4} in the above current 2.2Myuei.

On the other hand, in the first embodiment of the present invention, the error amplifier 103-2 increases the first and second currents I ₁ and I ₂ even when the first and second currents I ₁ and I ₂ are 0.5 μA. The voltage-current converter 103 is controlled so that the first and second currents I ₁ and I ₂ are balanced at 2.2 μA (that is, activated). In order to guarantee the start-up, the start-up current I ₄ is supplied to the voltage-current converter 103 so that the first and second currents I ₁ and I ₂ are 0.5 μA or more, and the first and second currents I ₁ , _{I 2} is a current above 2.2μA it is sufficient to stop the starting current _{I 4.}

  In the first embodiment of the present invention, the accuracy required for the start-up circuit 104 is greatly relaxed, and start-up can be guaranteed in a wider temperature range and a wider power supply voltage range than in the prior art.

Then, when the first diode D101-2 and second diodes D102-2 does not conduct, in the first current _{I 1} and the small-current region of the second current _{I 2,} the input signal _{V B} of the error amplifier 103-2 - The principle of increasing the absolute value of _VA compared to the prior art will be described.

In the conventional technique (k = 1 in Equation 1), in the small current region of the first current I ₁ and the second current I ₂ where the first diode D 101-2 and the second diode D 102-2 are not conducted, I ₂ × R _{Since 3} −I ₁ × R ₁ = 0, the input signal V _B −V _A becomes zero.

On the other hand, as shown in Formula 2, in Example 1 of the present invention, (1−k) × I ₂ × R ₂ is obtained, and the larger the k is, the more negative the absolute value. A large input signal V _B -V _A is obtained.

According to the first embodiment of the present invention, by setting I ₁ × R ₁ = k × I ₂ × R ₂ (k> 1), the requirement regarding the accuracy of the starting current I ₄ is alleviated, and the starting circuit 104 is When the first and second currents I ₁ and I ₂ are so small that the voltage-current conversion unit 103 does not perform a desired operation, the first and second currents I ₄ are supplied by supplying the starting current I ₄ to the voltage-current conversion unit 103. ₁ and I ₂ are increased, and when the first and second currents I ₁ and I ₂ are so large that the voltage-current converter 103 performs a desired operation, the third current I ₃ is supplied to the starting circuit 104. because off the starting current I _4, it is possible to ensure the startup of the constant current circuit without depending on the rising characteristics of and the power supply voltage without using a control signal supplied from the outside.

  Next, a second embodiment of the present invention will be described. The second embodiment of the present invention is an example of a constant current circuit in which a temperature characteristic adjusting resistor 205 is added to the first embodiment of the present invention. In addition, the description about the content similar to Example 1 of this invention is abbreviate | omitted.

  FIG. 6 is a circuit diagram showing a circuit configuration of a constant current circuit according to the second embodiment of the present invention.

  The constant current circuit according to the second embodiment of the present invention includes a first circuit 201, a second circuit 202, a voltage / current converter 203, a starting circuit 204, and a temperature characteristic adjusting resistor 205.

  The first circuit 201, the second circuit 202, the voltage / current converter 203, and the startup circuit 204 are the same as the first circuit 101, the second circuit 102, the voltage / current converter 103, and the startup circuit 104 according to the first embodiment of the present invention. Therefore, explanation is omitted.

  The temperature characteristic adjusting resistor 205 is commonly used between the first resistance element R201-1 of the first circuit 201 and the power supply (GND) and between the second resistance element R202-1 of the second circuit 202 and the power supply (GND). Is provided.

  Since the operation principle of the circuit excluding the temperature characteristic adjusting resistor 205 is the same as that of the first embodiment of the present invention, description thereof is omitted.

According to the resistance value of the temperature characteristic adjusting resistor 205, the temperature characteristic of the output current changes. That is, by changing the resistance value of the temperature characteristic adjusting resistor 205, the temperature characteristic of the output current _IOUT can be adjusted.

  According to the second embodiment of the present invention, the change in the value of k due to the adjustment can be reduced as compared with the case where either the first resistance element R201-1 or the second resistance element R202-1 is adjusted. .

  Further, according to the second embodiment of the present invention, the temperature characteristic adjusting resistor 205 is provided between the first resistance element R201-1 and the second resistance element R201-1 and the power supply (GND), so that the intermediate potential is set. Compared with the case where the temperature characteristic adjusting resistor 205 is provided, side effects when the temperature characteristic adjusting resistor 205 is switched by an analog switch can be reduced.

It is a circuit diagram which shows the circuit structure of the constant current circuit which concerns on Example 1 of this invention. 3 is a circuit diagram showing a circuit configuration of a voltage / current converter 103. FIG. It is a graph which shows the temperature characteristic which concerns on Example 1 of this invention, and a prior art. 6 is a graph showing the relationship between the first and second currents I ₁ and I ₂ of the voltage-current conversion circuit 103-1 and the input voltages V _A and V _B of the error amplifier 103-2 for each temperature when k = 1.05. is there. It is a graph showing a first embodiment and related input signals _V B -V _A conventional first and second current according to a technique _I 1, _{I 2} and the error amplifier 103-2 of the present invention when the -40 ° C.. It is a circuit diagram which shows the circuit structure of the constant current circuit which concerns on Example 2 of this invention.

Explanation of symbols

101, 201 1st circuit 101-1, 201-1 1st resistance element 101-2, 201-2 1st diode 102, 202 2nd circuit 102-1, 202-1 2nd resistance element 102-2, 202- 2 2nd diode 102-3, 202-3 3rd resistance element 103,203 Voltage current conversion part 103-1, 203-1 Voltage current conversion circuit 103-2, 203-2 Error amplifier 104,204 Starting circuit 104-1 , 104-2, 204-1, 204-2 MOS transistors 104-3, 204-3 Bias circuit 205 Temperature characteristic adjusting resistor

Claims (5)

A first circuit including a first resistance element and a first diode;
A second circuit including a second resistance element, a second diode, and a third resistance element connected in series with the second diode;
A voltage-current converter for supplying a first current to the first circuit, supplying a second current to the second circuit, and outputting a third current;
A startup circuit that controls on / off of the startup current according to the third current and supplies the voltage to the voltage-current converter,
The voltage-current converter is connected to convert a potential difference between the first circuit and the second circuit into a current,
The voltage-current converter increases the first current to the third current according to the startup current,
A constant current circuit, wherein a product of an element value of the first resistance element and the first current is larger than a product of the element value of the second resistance element and the second current. The first resistance element is connected in parallel with the first diode,
The constant current circuit according to claim 1, wherein the second resistance element is connected in parallel with a series circuit including the second diode and the third resistance element. Further equipped with a temperature characteristic adjusting resistor for adjusting the temperature coefficient,
The constant current circuit according to claim 1, wherein the first and second resistance elements are connected in series with the temperature coefficient adjusting resistor.   The voltage-current conversion unit includes an error amplifier and a voltage-current conversion circuit, and the third current has a current value such that an input voltage difference is larger than an offset voltage of the voltage-current conversion circuit in an input voltage characteristic of the error amplifier. The constant current circuit according to claim 1, wherein the constant current circuit is supplied to the starting circuit.   The start circuit includes a current output circuit and a plurality of MOS transistors connected in series with the current output circuit, supplies the start current through the plurality of MOS transistors, and the plurality of MOS transistors by the voltage-current converter. 5. The constant current circuit according to claim 1, wherein the start-up current is turned off when the third current larger than the output current of the current output circuit is supplied to a connection point of the transistor.

Images