Patent Grant
11402863
This application claims priority to Japanese Patent Application No. 2019-138412, filed on Jul. 29, 2019, the entire content of which is incorporated herein by reference.
The present invention relates to a reference voltage circuit.
Hitherto, a reference voltage circuit has been widely used in an electronic circuit in which the reference voltage circuit generates a reference voltage used as a threshold voltage in a comparator, which compares a given voltage with the threshold voltage.
A configuration including a Zener diode, a diode, and resistors can be employed in the reference voltage circuit because a reference voltage can be generated from a simple configuration (see, for example, Japanese Patent Application Laid-Open No. S49-128250).
In a conventional reference voltage circuit 100 illustrated in
The reference voltage circuit 100 thereby supplies an output voltage Vout for a reference voltage from a connection point between the resistors 107 and 106.
In the reference voltage circuit 100, the output voltage Vout is given by Equation (A1).
Vout=(R106·Vz+R107·VD)/(R106+R107) (A1)
In Equation (A1) above, Vz is a voltage at a cathode of the Zener diode 104, VD is a voltage at an anode of the diode 105, and R106 and R107 are resistance of the resistors 106 and 107, respectively.
Further, the current I105 flowing through the diode 105 is given by Equation (A2).
I105=(Vz−VD)/(R106+R107) (A2)
In Equation (A2), the voltage Vz has a positive temperature coefficient, and the voltage VD has a negative temperature coefficient.
If temperature coefficients of the resistors 106 and 107 are 0 (if the resistors 106 and 107 have no temperature dependence), the current I105 has a positive temperature coefficient.
When the current supplied by the constant current source 103 is denoted by I103, the current I104 flowing through the Zener diode 104 is given by Equation (A3).
I104=I103−I105 (A3)
When the current I103 has no temperature dependence, since the current I105 has a positive temperature coefficient, the current I104 has a negative temperature coefficient.
That is, as the current I105 increases in accordance with temperature rise while the current I103 does not change, the current I104 relatively decreases. Thus, in the case of the reference voltage circuit 100, since the current I104 decreases in accordance with the temperature rise, the linearity of the voltage Vz with respect to the temperature change cannot be maintained.
To the contrary, even in a case where the current I105 increases by the temperature rising, the linearity of the voltage Vz with respect to the temperature change can be maintained, and the temperature coefficient of the output voltage Vout can be brought to 0 by increasing the current I103 in order to reduce the influence of the negative temperature coefficient of the voltage VD.
However, in order to maintain the linearity of the voltage Vz, constant flow of the current I103 which is large enough to reduce the influence of the negative temperature coefficient of the voltage VD should be supplied through the Zener diode 104 as a bias current, making the reduction of the power consumption of the reference voltage circuit difficult.
The present invention has an object to provide a reference voltage circuit capable of maintaining a linearity of a temperature dependence of the voltage applied to the cathode of the Zener diode without increasing the current flowing from a constant current source to the Zener diode, and thus capable of saving power through reduction of power consumption.
According to an embodiment of the present invention, a reference voltage circuit includes a Zeller diode having a cathode connected to a current source via a first node, and an anode connected to a ground point; a first resistor having one end connected to the first node; a second resistor having one end connected to another end of the first resistor; a first diode having an anode connected to another end of the second resistor via a second node, and a cathode connected to the ground point; and a current control circuit which generates a control current corresponding to an anode voltage of the first diode so that the current source to supplies a reference current corresponding to the control current to the first diode.
According to the reference voltage circuit of the present invention, the reference voltage circuit capable of maintaining the linearity of the temperature dependence of the voltage applied to the cathode of the Zener diode without increasing the current flowing from the constant current source to the Zener diode, and thus capable of saving power through reduction of power consumption can be provided.
Now, description is given of embodiments of the present invention with reference to the drawings.
A reference voltage circuit 1 includes a current mirror circuit 10, a current control circuit 20, a resistor 31 (first resistor), a resistor 32 (second resistor), a Zener diode ZD, and a diode D1.
The current mirror circuit 10 includes p-channel transistors 11 and 12. A drain of the transistor 11 is connected to an output terminal To, and a drain of the transistor 12 is connected to an input terminal Ti.
The current control circuit 20 is a current source in the reference voltage circuit 1, and includes an error amplifier circuit OP1, a transistor 21, and a V/I conversion element 22.
The Zener diode ZD has a cathode connected to the output terminal To of the current mirror circuit 10, and an anode connected to the ground point.
The resistor 31 has one end connected to the cathode of the Zener diode ZD, and the other end connected to one end of the resistor 32 and an output terminal Tvout. The other end of the resistor 32 is connected to the anode of the diode D1. The cathode of the diode D1 is connected to the ground point.
The transistor 21 is an n-channel transistor. The transistor 21 includes a drain connected to the input terminal Ti of the current mirror circuit 10, a gate connected to an output terminal of the error amplifier circuit OP1, and a source connected to one end of the V/I conversion element 22.
The error amplifier circuit OP1 includes a non-inverting input terminal connected to the anode of the diode D1, and an inverting input terminal connected to the one end of the V/I conversion element 22.
The other end of the V/I conversion element 22 is connected to the ground point to convert a voltage VD of the diode D1 into a control current Icon.
Between the one end and the other end of the V/I conversion element 22, the diode 22A, the resistor 22B, and a series circuit including the resistor 22C and the diode 22D are connected in parallel. In this case, the diodes 22A and 22D are connected in a forward direction along the one end to the other end of the V/I conversion element 22.
In the reference voltage circuit 1, when the sources of the transistors 11 and 12 are applied with a power supply voltage VDD, the output voltage Vout is supplied from the output terminal Tvout.
At this time, a current IZD flowing through the Zener diode ZD generates a voltage VZ as a reverse voltage at the cathode of the Zener diode ZD. Further, a current ID1 flowing through the diode D1 generates a voltage VD as a forward voltage at the anode of the diode D1.
The output voltage Vout is determined in accordance with the voltage VZ, the voltage VD, and a voltage dividing ratio of the resistors 31 and 32. In Equation (1) below, the resistance of the resistors 31 and 32 are R31 and R32, respectively.
Vout=(R32·VZ+R31·VD)/(R31+R32) (1)
Then, the voltage VZ of the Zener diode ZD is adjusted to have a positive temperature coefficient so as to balance with the negative temperature coefficient of the voltage VD of the diode D1 so that the output voltage Vout of the reference voltage circuit 1 has no temperature dependence temperature coefficient is zero). The resistance R31 and R32 of the resistors 31 and 32 are thus set to satisfy Equation (2) below in a case where the current IZD flowing through the Zener diode ZD is supplied as a bias current.
R32·(dVZ/dT)+R31·(dVD/dT)=0 (2)
In Equation (2) above, (dVZ/dT) represents an amount of change of the cathode voltage VZ per unit temperature change and has a positive temperature coefficient. Further, (dVD/dT) represents an amount of change of the voltage VD per unit temperature change and has a negative temperature coefficient.
The current control circuit 20 functions as a V/I converter circuit which converts the voltage VD of the diode D1 into a corresponding control current Icon.
That is, the error amplifier circuit OP1 causes the transistor 21 to perform negative feedback processing so that the voltage drop of the V/I conversion element 22 becomes equal to the voltage VD. The control current Icon corresponding to the voltage VD thus flows through the V/I conversion element 22 from the input terminal Ti of the current mirror circuit 10.
The control current Icon is a combined current of currents flowing through the diode 22A, the resistor 22B, and the series connection of the resistor 22C and the diode 22D.
In this case, through the diode 22A, there flows a current I22A which is determined by the area ratio (area ratio of P/N junction) between the diode 22A and the diode D1 and is proportional to the current ID1. The voltage drop of the diode 22A has a negative temperature coefficient.
Further, through the resistor 22B, a current I22B (=VD/R22B) proportional to the voltage VD of the diode D1 flows. R22B is a resistance of the resistor 22B. The current I22B has a negative temperature coefficient.
Through the resistor 22C and the diode 22D, a current I22C (=ΔVD/R22C) proportional to the difference voltage ΔVD between the anode voltage of the diode D1 and the anode voltage of the diode 22D flows. R22C is a resistance of the resistor 22C. The difference voltage ΔVD has a positive temperature coefficient.
In response to an input of the control current Icon to the input terminal Ti from the current control circuit 20, the current mirror circuit 10 supplies a reference current Icrt to the Zener diode ZD and the diode D1 from the output terminal To in accordance with the predetermined mirror ratio. For example, in a case where the mirror ratio of the output current with respect to the input current is K, the reference current Icrt is given by Equation (3) below.
Icrt=K·(I22A+I22B+I22C) (3)
For example, in a case where the area ratio between the diode D1 and the diode 22A is 1:1, the area ratio between the diode at and the diode 22D is 1:N (>1, for example, 2 or more), and K=1 holds, the reference current Icrt is given by Equation (4) below.
Icrt=I22A+VD/R22B+ΔVD/R22C (4)
where I22A=ID1 holds.
In Equation (4), the first term I22A is a current flowing through the diode 22A having a characteristic similar to that of the diode D1 and is the same as the current ID1 flowing through the diode D1. The current ID1 is supplied from the output terminal To of the current mirror circuit 10 to the diode D1 as a feedback corresponding to the voltage VD.
Thus, the second term VD/R22B and the third term ΔVD/R22C are currents supplied from the output terminal To of the current mirror circuit 10 to the Zener diode ZD.
The current IZD flowing through the Zener diode ZD is given by Equation (5) which is obtained by excluding the first term from Equation (4).
IZD=VD/R22B+ΔVD/R22C (5)
As is understood from Equation (5) above, the first term and the second term represent currents flowing through the resistor 22B and the series circuit of the resistor 22C and the diode 22D, respectively, and are thus not affected by the current ID1 flowing through the diode D1.
Further, in a case where the temperature coefficients of the resistors 22B and 22C are zero, the temperature coefficient of the current VD/R22B is negative because the voltage VD has a negative temperature coefficient, and the temperature coefficient of the current ΔVD/R22C is positive because the difference voltage ΔVD has a positive temperature coefficient. Thus, through adjustment of the resistance R22B of the resistor 22B and the resistance R22C of the resistor 22C, the temperature characteristic of the current IZD flowing through the Zener diode ZD can be arbitrarily adjusted to be positive or negative.
As described above, the reference voltage circuit 1 generates the control current Icon by combining the current corresponding to the voltage VD and the current corresponding to the current IZD flowing through the Zener diode ZD, supplies the reference current Icrt from the current mirror circuit 10 in accordance with the control current Icon, and adjusts the currents ID1 and IZD in accordance with the temperature change.
As described above, in accordance with variation that is based on the temperature dependence of each of the voltage VD and the voltage VZ, the current ID1 which compensates this variation is supplied to flow through the diode D1, and the current IZD is supplied to flow through the Zener diode ZD, permitting arbitrary control of the voltage VZ.
Since the reference voltage circuit 1 is capable of supplying the current IZD in response to the temperature change with adjustment to the minimum necessary current amount, the reference voltage circuit 1 is thus capable of saving power while maintaining the linearity of the temperature dependence of the voltage VZ applied to the cathode of the Zener diode ZD.
The reference voltage circuit 1 may include a start-up circuit (not shown) to apply a predetermined pulse current to the resistor 31 at the time of start-up.
Further, the V/I conversion element 22 has been described as a configuration including the diode 22A, the resistor 22B, the resistor 22C, and the diode 22D, but the V/I conversion element 22 may be a configuration including any one of the diode 22A, the resistor 22B, and the series circuit of the resistor 22C and the diode 22D, or a combination thereof. In the case of such configuration, in order to maintain the linearity of the cathode voltage VZ, the mirror ratio of the current mirror circuit 10, the area ratios of the diodes 22A and 22D, and the resistances of the resistors 22B and 22C are adjusted, and the control current Icon is generated from the voltage VD so that the sum of the currents ID1 and IZD become the current Icrt that is adjusted as appropriate in accordance with the temperature change.
In a reference voltage circuit 1a a diode D2 is added to the configuration of
Vout=(R32·(VZ−VD2)+R31·VD)/(R31+R32) (6)
Through addition of the diode D2, the voltage at the one end of the resistor 31 connected to the cathode of the diode D2 has a positive temperature coefficient because the anode voltage of the diode D2 has a negative temperature coefficient. The voltage at the one end of the resistor 31 thus changes in accordance with the temperature change.
Since the voltage at the one end of the resistor 31 has a positive temperature coefficient, in order to eliminate the temperature dependence of the output voltage Vout, the resistance R31 of the resistor 31 is increased, as is understood from Equation (6). As a result, the voltage drop of the resistor 31 increases, and the output voltage Vout decreases.
Thus, as compared to the configuration of
Further, as illustrated in
For example, by the addition of the constant current source 41 to the cathode of the Zener diode ZD, the Zener diode ZD is supplied with the current IZD from the constant current source 41. As a result, the current mirror circuit 10 supplies the reference current Icrt as the current ID1 flowing through the diode D1. In this case, the current IZD flowing through the Zener diode ZD is not affected by the voltage VD, and the current control circuit 20 compensates only the current ID1 flowing through the diode D1 in accordance with the temperature change.
The V/I conversion element 22 thus has, for example, a configuration including only the diode 22A illustrated in
Further, also in a case where the constant current source 42 is added to the input terminal Ti of the current mirror circuit 10, similarly to the above-mentioned case in which the constant current source 41 is added, the current control circuit 20 compensates only the current ID1 flowing through the diode D1.
A reference voltage circuit 1A includes a current source 10A, a current control circuit 20A, resistors 31 and 32, a Zener diode ZD, and a diode D1.
The current source 10A includes a p-channel transistor 13.
The current control circuit 20A includes an error amplifier circuit OP2, a V/I conversion element 22, and a transistor 23.
The transistor 13 includes a source to which a power supply voltage VDD is applied, a gate connected to the output terminal of the error amplifier circuit OP2 and the gate of the transistor 23, and a drain connected to the cathode of the Zener diode ZD and one end of the resistor 31.
The transistor 23 is a p-channel transistor. The transistor 23 includes a source to which the power supply voltage VDD is applied, and a drain connected to one end of the V/I conversion element 22 and the non-inverting input terminal of the error amplifier circuit OP2.
The V/I conversion element 22 has another end connected to the ground point.
The resistor 31 has another end connected to the output terminal Tvout and one end of the resistor 32.
The resistor 32 has another end connected to the anode of the diode D1 and the inverting input terminal of the error amplifier circuit OP2.
The anode of the Zener diode ZD is connected to the ground point.
The cathode of the diode D1 is connected to the ground point.
The current control circuit 20A functions as a V/I converter circuit to convert a voltage VD of the diode D1 into a control current Icon corresponding to the voltage VD.
The voltage drop of the V/I conversion element 22 is substantially equal to the voltage VD of the diode D1 due to the negative feedback of the transistor 23 because the error amplifier circuit OP2 and the transistor 23 form a voltage follower.
Thus, through the V/I conversion element 22, the control current Icon flows through the transistor 23 as a current corresponding to the voltage VD of the diode D1.
A drain current corresponding to the aspect ratio flows through each of the transistors 13 and 23 because the transistors 13 and 23 have the same gate voltage. As a result, a reference current Icrt corresponding to the control current Icon flowing through the V/I conversion element 22 flows through the transistor 13.
As described above, similarly to the first embodiment, the reference voltage circuit according to the second embodiment generates the control current Icon from the anode voltage VD varying depending on the temperature change, to thereby supply, in accordance with the control current Icon, the reference current Icrt which is a combined current of the current ID1 flowing through the diode D1 and the current IZD flowing through the Zener diode ZD, from the transistor 13.
Since the reference voltage circuit according to the second embodiment is capable of supplying the current IZD in accordance with the temperature change with the current IZD which is adjusted to the minimum necessary current amount, the reference voltage circuit is thus capable of saving power while maintaining the linearity of the temperature dependence of the voltage VZ which is applied to the cathode of the Zener diode ZD.
A reference voltage circuit 1B has a configuration similar to that of the second embodiment except that the reference voltage circuit 1B includes a current control circuit 20B.
The current control circuit 20B includes p-channel transistors 24 and 25, n-channel transistors 26 and 27, and a V/I conversion element 22.
The transistor 24 includes a source to which the power supply voltage VDD is applied, a gate connected to the gate and the drain of the transistor 25, and a drain connected to the drain and the gate of the transistor 26.
The transistor 25 includes a source to which the power supply voltage VDD is applied, and the drain connected to the drain of the transistor 27.
The transistor 26 includes the gate connected to the gate of the transistor 27, and a source connected to the anode of the diode D1.
The transistor 27 includes a source connected to the ground point through the V/I conversion element 22.
The current control circuit 20B functions as a V/I converter circuit to convert a voltage VD of the diode D1 into a control current Icon corresponding to the voltage VD.
The transistors 24 and 25 form a current mirror, and the current corresponding to a mirror ratio between the transistors 24 and 25 flows through each of the transistors 26 and 27 so as to determine the source voltage of the transistor 27.
For example, in a case where the mirror ratio between the transistors 24 and 25 is 1:1, and the transistors 26 and 27 have the same aspect ratio, the same drain current flows through each of the transistors 26 and 27. The source voltage (voltage VD) of the transistor 26 thereby become equal the source voltage of the transistor 27. That is, the voltage drop of the V/I conversion element 22 becomes substantially equal to the voltage VD.
Since the control current Icon corresponding to the voltage VD flows through the V/I conversion element 22 via the transistor 25, a reference current Icrt corresponding to the mirror ratio with respect to the control current Icon flowing through the V/I conversion element 22 flows through the transistor 13 forming a current mirror with the transistor 25.
As described above, the reference voltage circuit 1B generates the control current Icon based on the voltage VD varying depending on the temperature change, to thereby supply, in accordance with the control current Icon, the reference current Icrt which is a combined current of the current ID1 flowing through the diode D1 and the current IZD flowing through the Zener diode ZD, from the transistor 13.
Since the reference voltage circuit 1B is capable of supplying the current IZD in accordance with the temperature change with the current IZD which is adjusted to the minimum necessary current amount, the reference voltage circuit 1B is thus capable of saving power while maintaining the linearity of the temperature dependence of the voltage VZ applied to the cathode of the Zener diode ZD.
A reference voltage circuit 1C has a configuration similar to that of the first embodiment except that the reference voltage circuit 1C includes a current control circuit 20C, a bipolar transistor BT1, and a constant current source 41.
The current control circuit 20C includes a bipolar transistor BT2.
The bipolar transistors BT1 and BT2 are npn-type bipolar transistors and form a current mirror.
The bipolar transistor BT1 includes a collector connected to a base of the bipolar transistor BT1 and the other end of the resistor 32, and an emitter connected to the ground point. That is, the bipolar transistor BT1 corresponds to the diode D1 in the first embodiment.
The bipolar transistor BT2 includes a collector connected to the input terminal Ti of the current mirror circuit 10, a base connected to the base of the bipolar transistor BT1, and an emitter connected to the ground point. In this case, the base or the emitter of the bipolar transistor BT2 corresponds to the diode 22A of the V/I conversion element 22 in the first embodiment and has a diode characteristic similar to that of the base or the emitter of the bipolar transistor BT1.
In the bipolar transistor BT1, when the voltage VD is applied to the base, the base current flows corresponding to the voltage VD, and a collector current (current ID1) corresponding to the base current flows.
Through the bipolar transistor BT2, a collector current flows based on the mirror ratio between the bipolar transistor BT2 and the bipolar transistor BT1.
The collector current of the bipolar transistor BT2 is a control current Icon flowing in accordance with the voltage VD and is supplied to the input terminal Ti of the current mirror circuit 10.
The current mirror circuit 10 thereby supplies the reference current Icrt corresponding to the mirror ratio from the output terminal To.
Here, when the mirror ratio of the current mirror circuit 10 is 1:1, and the mirror ratio between the bipolar transistors BT1 and BT2 is 1:1, the reference current Icrt supplied from the output terminal of the current mirror circuit 10 becomes substantially equal to the current ID1.
Since the current IZD flowing through the Zener diode ZD is thus supplied from the constant current source 41 and is not affected by the voltage VD, the current control circuit 20C compensates only the current ID1 flowing through the diode D1 at the bipolar transistor BT1.
Further, also in a case where the constant current source 42 is added to the input terminal Ti of the current mirror circuit 10, similarly to the above-mentioned case in which the constant current source 41 is added, the current control circuit 20C compensates only the current ID1 flowing through the bipolar transistor BT1 (corresponding to the diode D1) in which the collector and the base are connected.
As described above, the reference voltage circuit 1C is configured to generate the control current Icon corresponding to the voltage VD in the diode connection of the bipolar transistor BT1, to thereby cause, in accordance with the control current Icon, the reference current Icrt to flow from the transistor 13 to adjust the current ID1 in accordance with the temperature change.
Thus, since the reference voltage circuit 1C is capable of supplying the current IZD in accordance with the temperature change with the current IZD being adjusted to the minimum necessary current amount, the reference voltage circuit 1C is capable of saving power while maintaining the linearity of the temperature dependence of the voltage VZ to be applied to the cathode of the Zener diode ZD.
The embodiments of the present invention have been described above in detail with reference to the drawings. However, specific configurations of the present invention are not limited to the embodiments and encompass designs, modifications, and the like without departing from the gist of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2019-138412 | Jul 2019 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3916508 | Conzelmann et al. | Nov 1975 | A |
| 6806749 | Drusenthal | Oct 2004 | B2 |
| 7071672 | Drusenthal | Jul 2006 | B2 |
| 7554311 | Pan | Jun 2009 | B2 |
| 8461912 | Kumar | Jun 2013 | B1 |
| 8575999 | Akiya | Nov 2013 | B2 |
| 20040041622 | Wu | Mar 2004 | A1 |
| Number | Date | Country |
|---|---|---|
| S49-128250 | Dec 1974 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20210034092 A1 | Feb 2021 | US |
