TW434992B - Current source apparatus with temperature compensation function - Google Patents

Abstract

A kind of current source apparatus having temperature compensation function can be used for any fabricating process that includes CMOS, BJT, HBT, GaAs, ..., and so on. By using simple devices, such as Schottky diode, resistor, and depletion type FET transistor, to match the special symmetrical-circuit structure, the compensation of temperature variation can be performed in order to decrease the influence of temperature on current such that the product yield of total fabricating process is improved.

Description

4349924. V. Description of the invention (1) The present invention relates to a current source device having a temperature compensation function. 'Λ; 89Ji./t4':!: A current source 1 ^ is set, especially for a type. Figure 1 shows a current source with a positive temperature change. The two PMOS transistors (PI, P2) at the top of Figure 1 constitute a current source, and the currents on the left and right sides are equal (1, 12). Therefore, the gate-source voltage of the NMOS transistors Q1 and Q2 is jointly (Vgs) are equal, so the voltage at point A is equal to the voltage at point B. For the analysis of the line in Figure 1 for the current part, we can get the following formula β ¢ 1) I〆 = VeB4-Veb3 IL ξ Is3 exp (VEB3 / VT) (2) I2 s Is4 exp (VEB4 / VT) ( 3) llR Ξ VT ^ n (I2 / Is4) -νΊίη {ΙλΙ1ί2) and I [=: I2.,. ^ VT / R ^ n (N) (4) where N is the BJT transistor Q3 and Q4 Size ratio. From the above formula (4), it can be known that the current values I 1 and I 2 of the current source in FIG. 1 are only related to the size ratio of the BJT transistors Q1 and Q 2 and the resistance value R; because the value of VT increases with temperature Increased, so the current values I 丨 and 12 also increase with the increase in temperature, so they show a positive change, which is called the PTAT current source. If this current source is supplied to the working circuit in the form of a current mirror via re f_C, the entire working circuit will show a positive temperature change. In terms of the above process, components such as PMOS, NMOS, BJT transistors and resistors need to be provided. However, in the GaAs process, due to cost and implementation considerations, generally only only a few basic components are provided, such as empty type_

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Zi Zheng 4 3 ^ .9 9 2 ^ V. Description of the invention (2) I ¢ 1 ^ t: | (depletion type) MOS ί ^ ΤΤ "!; Crystal, Schottky diode, resistor, and empty type ( The depletion type) M0SFET transistor only provides N type, so the current source of the architecture shown in Figure 1 may not be implemented by the GaAs process. In addition, the current source shown in Figure 1 uses the size ratio of two BJT transistors (Q3, Q4) to adjust the currents I and 12. This adjustment method is not commonly used in the GaAs process, and the BJT transistor consumes a considerable amount of circuit area, which also reduces the design efficiency. In view of this, the object of the present invention is to propose a current source device with a temperature compensation function in order to improve the above problems, which can be applied to any process, including CMOS, B JT, HBT, GaAs, etc., using simple components such as Schottky Diodes, resistors, and transistors, combined with a special symmetrical circuit architecture, make it possible to compensate for temperature changes to reduce the effect of temperature on current, thereby improving the yield of the overall process and the area of the circuit. In order to achieve the above-mentioned object, the structure of the current source device with temperature compensation function provided by the present invention includes the following units. A first current source unit provides a first current with a constant current value and a second current source unit provides a second current, the current value of which increases with increasing temperature. The second current source unit includes at least: a first transistor, a first second current; a second electrode, which constitutes a first current path through the transistor, and a second diode, which constitutes a The second current path passes the second current; the value of the second current depends on the size ratio between the first diode and the second diode.

43Λ9 92; 4_ V. Description of the invention (3) 'A third current source unit provides a third current whose value is the difference between the first current and the second current; wherein the first current source unit The second current source unit is connected in series, and the third power source unit is connected in parallel to the third power source unit. Brief description of the drawings: In order to make the above-mentioned objects, features, and advantages of the present invention more comprehensible, a preferred embodiment is given below and described in detail with the accompanying drawings as follows: FIG. 1 shows a Current source with positive temperature change; Figure 2 shows a current source for a possible GsAs process; Figure 3 shows the current-voltage map of the diode and the load line of the GaAs transistor; Figure 4 shows the use of a current mirror (current Mirror), a schematic diagram of the architecture for coupling current to a complex stage circuit; Figure 5 shows a schematic diagram of a current source based on a GaAs process and a PTAT current source that changes positively with temperature; Figure 6 shows an embodiment of the present invention Schematic diagram of the circuit architecture; FIG. 7 shows a detailed circuit diagram of an embodiment of the present invention; FIG. 8 shows an application diagram for coupling output of the current generated by the device of the embodiment of the present invention; and FIG. 9 shows the E and F of FIG. 8 Partially combined into a current source; Figure 10 shows the application of the structure of the present invention, in the case of only NMOS and diode, a voltage source that does not change with temperature Road;

434B924 Five 'invention description (4); Figure 11 is the experimental simulation data of the BB circuit in Figure 10 and its current vs. temperature; Figure 12 is the BB circuit in Figure 10, The experimental data of its current vs. voltage Vcc; among them, when the diode ratio is 2: 1, the current versus voltage relationship is A curve, and when the diode ratio is 8: 1, the current versus voltage relationship is B curve; Figure 13 shows the experimental data graph of the general current source and its current versus temperature change; and Figure 14 shows when the BB part in Figure 10 and the circuit in Figure 13 are combined into a current source (as shown in Figure 9) Part E, F), the experimental data chart of its current versus temperature change. Symbol Description:

Vcc ~ voltage source; P2 P2 ~ PMOS transistor, CU-Q2, Q5-Q6 ~ FET transistor; Q3-Q4 ~ BJT transistor; R ~ resistor; D1-D2 ~ diode; 1 u — 1 ts ~ current source; A1 first current source unit; A2 ~ second current source unit; A3 ~ third current source unit; Pa-Pb ~ current path; first current path; P2 ~ second current path; P3 ~ The third current path; P4 ~ the fourth current path; IaI- Ia2 ~ constant current; Ibl-Ib2 ~ current that changes positively with temperature;

Ici-Ic2 ~ current; Ma, Mb, Ml, M2, M3, M4 ~ (empty type) N-1 ype FET transistor; E, F ~ coupling current source. Example: _ Please refer to the circuit in Figure 2. It is a constant current source using GsAs process. It is mainly composed of empty FET transistors (Q5, Q6), Schottky diodes (D1, D2), resistor R. Made up. The current source shown in Figure 2 is self-biased

434992 ^ V. Description of the invention (5) (self-bias) The structure uses diode D1 (D2) to raise the voltage of Q5 (Q6) source and ground the gate of Q5. The diode is not used here because the area occupied by the diode is much smaller than the area occupied by the resistor under the same current. In addition, from the load diagram in Fig. 3, it can be seen that the operating point current (iD, VD) 'composed of the transistor Q5 (Q6) and the diode D1 (D2) is the operating point current when the voltage source Vcc varies greatly. The change is not large. Since Q5 = Q6, D1 = D2, and the gates on both sides are equipotential, in order to make the gate-source voltage (Vgs) of Q5 and Q6 equal, it must be ι = 〖2. In addition to using the current 12 of this current source for other circuits (loads) (as shown in Figure 2); you can also use a current mirror (Clirrent mirror) method to 'couple current to a complex stage circuit, as shown in Figure 4 As shown. In Figure 4 (a) and (b), 'I! Current is coupled to the (ni) stage circuit, where' the size of each transistor Q2 ~ Qn is equal to Q1, then the total area of the diode Dt is equal to the original Η times the area of diode D1 in the current source. In addition, if coupling (η-1) times L current for other circuits, the area of transistor Qn must be (n-1) times Q1 'and the area of diode Dn must also be (n-1 ) Times, as shown in Figure 4 (c). The above current sources can be applied to general differential pairs to improve their CMRR (same mode rejection ratio) and PSRIi (power supply rejection ratio). The current source mentioned above (according to the GaAs process) is matched with a PTAT current source that changes in a positive direction with temperature and deformed to obtain the circuit shown in Figure 5. In Fig. 5, transistors Q3 and Q4 have the same size, and the area of diode D3 is η times that of D4. In addition, the gates of Q3 and Q4 are no longer grounded to avoid

4 349 9 2¾ 5. Description of the invention (6) The current is limited by Q 3 and Q 4. 113 ^ 0 So first, the current source k = [u is made by the mechanism of the circuit, VgS of Q3 and Q4 are the same, so the following formula can be established

VD4 J1R 'V〇3 = 〇 => I, R = V ,,-V 1 D4 ν and h ^ ID3 exp (VD3 / VT) I2 = ID4 eXP (VD4 ^ VT)

IiR = VT ^ n (I2 / ID4)-VT ^ n (I1 / ID3)

Ij ^ vT / R ^ n (n) So far, it can be known that in the current source circuit shown in Fig. 5, the current values ii and 12 are only related to the size ratio of the diodes D3 and D4 and the resistance value R; and The value of ντ increases with increasing temperature, so the current values 1 and 12 also increase with increasing temperature, and therefore show a positive change. This is called a PTAT current source. Therefore, as long as it is possible to make current sources Itl and It2 that do not use P-type transistors, the purpose of implementing a current source with temperature compensation function (that is, its current has a shape of η (η)) using the GaAs process can be achieved. However, referring to Fig. 5, if the current sources Iu and It2 are constant current sources, then as in Fig. 2, the current Iti (= ^) = 1 = 12. In this way, the current values of I, and 12 are determined by the constant current sources Itl (and It2), and are not affected by the size ratio of the diodes D3 and D4. Therefore, the current sources 1ti and 1 cannot use the conventional constant current source circuit. ~ Figure 6 shows the structure diagram of the current source device with temperature compensation function of the present invention. In this embodiment, a GaAs transistor is used for introduction;

434992 ^ _ V. Description of the invention (7) · The CTCs are all empty N-type FET transistors, and the diodes are Schottky diodes with high energy barriers. However, the present invention is not limited to the GaAs process, but can be applied to various possible semiconductor processes. Referring to Fig. 6, the present invention proposes a current source device having a temperature compensation function, which includes the following units. A first current source unit (A1) 'provides two current paths (p a,

Pb) 'respectively circulates current k and l having a constant current value. A first-current source unit (A2), which provides current (ibl and ib2) ', and its current value increases as the temperature increases. Wherein, the second current source unit (A2) at least includes: a first transistor (M1), a first diode (D1), constituting a first current path (P1) to flow the current (Ibl); -The second transistor (M2) and a second diode (D2) 'constitute a second current path (P2) through which the above-mentioned current (Ib2) flows. The bias transistor (gate) of the first transistor (M1) and the second transistor (M2) are coupled together, and the value of the current (Ibl = Ib2) depends on the first diode (D1) and The size ratio between the second diode (D2). In this embodiment, both the first transistor (M1) and the second transistor (M2) may be N-type FET transistors. A third current source unit (A3) provides a third current path (p3) and a fourth current path (P4) 'to flow currents (Icl and 1.2), respectively. One of the current paths (pa) in the first current source unit connects the first current path (P1) and the third current path (P3), and the other current path in the first current source unit (A1). (Pb) Lightly connect the second current path (P2) and the fourth current path (P4), and the value of the third current is

Page 10 434992 ^ V. Description of the invention (8) · The difference between the above first current and second current (Ici = Iai „Ibi; [^ -ib2). A As mentioned above, the circuit When a current source unit (A1) is a constant current source, the currents on its paths pa and pb 丨 a will not change due to changes in voltage at points X and γ. 'If there is no third current source unit (A3) With 'the second current source unit (A2), the currents Ibi and I ^ on paths P1 and P2 will be dominated by the first current source unit (A1). In this way, the currents (I μ and 込 2) will be It will not be determined by the ratio (η) of the diodes D1 and D2, that is, it will not have a characteristic proportional to VT / R € η (η). Therefore, in the present invention, the third current source unit (A3 The purpose of) is mainly to be used as a current sink. “The first current source unit (A1) of constant current can be applied to the present invention” and the current of the second current source unit (A2) (ibi * Ib2) It is still determined by the ratio (η) of diodes D1 and D2, and has the characteristic of positive change with temperature, that is, the relationship of Ibl = Ib2 = VT / R € η (η) In addition, the current (Icl and I.2) of the third current source unit (A3) is not a constant current source, but changes with the change in the voltage at the X and Y points. Figure 12 is shown in Figure 6. The experimental simulation data when the current source circuit architecture uses njjos. In Figure 12, when the ratio of the two diodes (n: 1: :) is changed from 2: 1 to 8: 1, the values of the remaining components can be changed accordingly. Under the circumstances, the curve of the current I changes from A to B ^ Therefore, the current value of the current I still depends on the ratio of the two diodes. In addition, it can be seen from the comparison of the curves A and β that the changes in the component and voltage source Vcc affect the current. The effect of the value is not large, so it can effectively increase the yield

Page 11 4 349 92 '^ 5. Description of the invention (9) Figure 7 shows a circuit diagram of an embodiment of a current source device with temperature compensation function in the present invention using a GaAs FET. The two current paths Pa and Pb in the first current source unit (A 1) are both composed of an empty NMOS transistor (Ma) _ connected to a diode (Da), and the diode ( The cathode of Da) is coupled to the gate (bias) of the transistor (Ma); one terminal of the transistor Ma is coupled to a voltage source (Vcc), and the two diodes Da in the two current paths are The cathodes are respectively coupled to the drains of the first transistor (M 1) and the second transistor (M2), as shown in FIG. 7. 0 The first current path pi in the second current source unit (A2). Is formed by connecting the first N-type FET transistor M1, the resistor R, and the first diode D1 in series with each other; and the second current path P2 is by the second N_type FET transistor M2 and the first The two diodes D2 are connected in series with each other, as shown in FIG. 7. The second current source unit A2 further includes a biasing device BA1 (refer to FIG. 6) for biasing the first transistor (M1) and the second transistor M2. See "", Fig. 7 'The above biasing device (bai) includes at least: a first biasing transistor Mbl connected in series with a voltage level shifting device (through a resistor Rb) disposed at the voltage source Vcc and The above-mentioned transistor M1 and the gate of the heart; L Φ Γ Ϊ piezoelectric crystal ^ 2 'is provided between the above-mentioned transistors M1 and 112 bias-pole and voltage reference point (GND).

The bias pole of Mbl is transferred to the above town _ Guangbao Chengce crystal basket to attack the connection point of the first electric solar element M2 and the first current source single alpha channel fe (Pb); the second bias transistor ,

Page 12 434992 ^ V. Description of the invention-The gate electrode is connected to the above voltage reference point. In this embodiment, the above-mentioned voltage level shifting device is formed by connecting two diodes (Dbll, Dbl2) in series; the second bias transistor l is further connected in series-the diode (DbZ1) recoupling Connect to the voltage reference point as shown in circle 7. Here, for the bias of the M1 and M2 gates, the present invention uses a level shift method instead of a resistor divider, which is to reduce the current leakage period of the current to the M1 and M2 gates. The current is as close to zero as possible. The third current path p3 in the third current source unit (A3) is formed by connecting an N-type FET transistor M3 and a diode D3 in series; the fourth current path P4 'is formed by an N- The type FET transistor M4 and the diode D4 are connected in series with each other; and the drains of the transistors M3 and M4 are coupled to the X point and the Y point, respectively, as shown in FIG. 7. In order to make the currents flowing in the current paths p 3 and p 4 the same, that is, 1 ^ = 1. Therefore, the sizes of the transistors M3 and [^ 4 are the same, and the sizes of the diodes D3 and D4 are the same. The third current source unit A3 further includes a biasing device "2 (not shown in Fig. 6) for biasing the gates of the transistors M3 and M2 connected to each other. In this embodiment, the bias The structure and configuration of the voltage device BA2 is the same as that of BA1, as shown in Fig. 7. Fig. 11 is the current source circuit shown in Fig. 7 (that is, part of the BB circuit in Fig. 10). Only NMOS is used in the transistor. In the case of the experimental simulation data, the value of the current I is the same as the result of the previous derivation, and it increases with the increase of temperature. Fig. 8 shows an application diagram for coupling and outputting the current generated by the device of the embodiment of the present invention. It can be seen that the part F is supplied to the circuit TA for use.

Page 13 434992 ^ Five 'description of the invention (11) ^ The current ITA (= m XD is a positive change with temperature. From the above, we can see that the barrier height of the diode decreases with increasing temperature, so it passes The current increases with increasing temperature; and the transistor decreases with increasing temperature. Therefore, the current portion, that is, A 丨, is less affected by temperature. However, because the F portion changes positively with temperature, Therefore, the current ITB (= k X lb2) used by the E supply circuit TB is the opposite and becomes a negative change with temperature. If the E and F parts are combined into a current source, as shown in Figure 9, it can be adjusted by The proportion of parts E and F, so that the current Γ supplied to the circuit T c does not change with temperature as much as possible 'or minimizes the effect of temperature on the current Ief ^. If the circuit TC is only a resistor, The voltage output by the resistor is a constant voltage that is not affected by temperature changes. Figure 14 shows the experimental data diagram of current versus temperature changes when E and F are combined into a current source. Figure 13 shows Shows the general current source, whose current changes with temperature The experimental data chart. From Figure 13 it can be seen that the current of the general current source is about 440 ν A at minus 40t; when the temperature rises to 80 t, the current is reduced to about 408 A, and the current variation reaches 32. A. As can be seen from Figure 14, 'the current source formed by combining parts E and F, the current at minus 40 is about 4 6 8. 7 Ren A; when the temperature rises to about 50 ° C, The current decreases to approximately 4 6 2 // A. When the temperature rises to 80, the current increases to approximately 4 64 // A; the maximum change in current during this time is only 6.7yA, which is far less than the average electricity. Current source. Therefore, the current source combined by parts E and F has indeed reduced the effect of temperature on the current IEF to a minimum, and has almost no change with temperature changes.

Page 14 4 349 9 2 ^ _ V. Description of the invention (12) Figure 10 shows the voltage source circuit that is designed not to change with temperature when the structure of the present invention is applied. In the case of only NMOS and diodes. In addition, by connecting part F into a circuit as shown in Fig. 10, it can be known from the above that the IF current is approximately equal to (VT / R) X βη (η) X m, then the voltage Vout at the Cout point is Vcc-IrxRF-VDr. Mu, v〇ut = Vcc- {(mVTRr / R) x € n (n) + VDr}. It is known that [(mVTRF / R) x / n (n)] shows a positive change with temperature, and VEF (diode voltage) damage shows a negative change with temperature. Therefore, as long as the value of (mRr / H) is adjusted appropriately, that is, An output voltage that does not change with temperature can be obtained. From the above, it can be known that the entire architecture of the current source device with temperature compensation function proposed by the present invention uses the concept of symmetrical proportions of components. Therefore, using the proposed structure of the present invention can not only be used in temperature compensation circuits. The output current is also determined using a symmetrical ratio, so it can be used in related circuits. Therefore, the performance of the circuit will not be affected by the process itself, so that the yield of circuits produced by processes such as GaAs ... will be improved. Although the present invention has been disclosed as above with a preferred embodiment, it is not intended to limit the present invention. 'Any person skilled in the art can make some changes and decorations without departing from the spirit and scope of the present invention. The scope of protection of the invention shall be determined by the scope of the attached patent application. 1 ^ 1 HHra p. 15

Claims (1)

4 349 92 ^ VI. Patent application scope 1-^ · Current source device with temperature compensation function, including: a first current source unit, providing two current paths, respectively, a first current with a constant current value; The second current source unit provides a second current whose current value increases as the temperature increases; wherein the second current source unit includes at least: a first transistor, a first diode, and a first component. A current path passes the second current; a second transistor and a second diode constitute a second current path to pass the second current; the value of the second current depends on the first diode and the first A size ratio between the two diodes; a third current source unit providing a third current path and a fourth current path, respectively, passing a third current; wherein the current path in the first current source unit is One is coupled to the first current path and the third current path, and another current path in the first current source unit is coupled to the second current path and the fourth current path. The first current and the second current value is the difference of the two second current. 2. The device according to item 1 of the scope of the patent application, wherein the two current paths in the first current source unit are each composed of a transistor connected in series with a diode, and the diode The cathode is coupled to the transistor; the-terminal of the transistor is connected to a voltage source; the cathodes of the two diodes in the above path are respectively coupled to the above-mentioned, electric voltage. In the device, one terminal of a transistor is coupled to the first current source unit-the second electric source path, 434992 VI. Scope of patent application: The anode of the first monopolar body is coupled to the other end of the first transistor, and the cathode is connected to a voltage reference point; one end of the second transistor is coupled to the first current source. In another current path of the unit, the anode handle of the second diode is connected to the other end of the second transistor, and the cathode is coupled to the voltage reference point, the bias electrode of both the first and second transistors. Connected to each other. 4. The device according to item 3 of the patent claim, wherein a resistor is further coupled between one end of the first transistor and the anode of the first diode. 5. The second current source unit according to item 2 or 3 of the scope of patent application further includes a device that is biased-negative: 辻, wherein the transistor and the second transistor are biased. I * 'is used for the above-mentioned 6.-The voltage device described in item 5 of the scope of patent application includes at least one device with a first bias voltage, wherein the above-mentioned bias device is disposed between the voltage source and the Z series. -A voltage level shifting electrode; and 'a second bias transistor ~ (or a second) transistor bias second) the transistor bias electrode and the voltage reference' are set at the first (or voltage) The bias electrode of the transistor is coupled between the first point; the connection point of the other current path of the first bias source unit is the transistor and the first current bias electrode are coupled to the voltage reference point. The second bias transistor 7. The voltage level shifting device as described in item 6 of the scope of the patent application is composed of a plurality of diodes. The voltage reference point is more stringed, or by a single diode. A pole is then lightly connected to the above 8. The device described in item 丨 of the scope of patent application 'wherein, the above $ 17Page 4 3 49 9? VI. Patent application scope Three current source unit * body, which constitutes the above-mentioned first body and a forty-two current, as mentioned above. The cathode of the electrode body is coupled to a first electrode of the first current source and the second reference point is coupled to the above-mentioned second reference point. At least the zeta current pole body, and the other transistor of the anode voltage reference element connected to the third and second range include: a first electric body and a third dipole path. The third current passes through to form the fourth current path. The device according to item 8 in which the bias voltages of the two current-transistor transistors are mutually interchanged, wherein one of said first current source units is electrically coupled to another point of said third transistor; a current path of one of said fourth transistor 'The other end of the aforementioned fourth two' has a cathode coupling (connected to a fourth electrical connection of the above-mentioned first phase connection.) In the above-mentioned current flow path, one end, its end is coupled to the anode of the upper pole and the above-mentioned voltage 10. The device according to item 9, the second current source unit further includes a biasing device for biasing the second transistor and the fourth transistor. The second transistor 11. The device according to item 10 of the scope of patent application Wherein, the biasing device includes at least: a third biasing transistor connected in series with an electro-ink 'position device' disposed between the voltage source and the third (or fourth) transistor t voltage electrode; and, A fourth bias transistor , Set between the second (or fourth) transistor bias electrode and the voltage reference point; the bias electrode of the first bias transistor is coupled to the first transistor and the second-second source unit The connection point of the other current path; the bias electrode of the fourth bias transistor is coupled to the voltage reference point. 12. The device according to item 11 of the scope of patent application, wherein the above .. voltage level The quasi-shifting device is connected by a plurality of diodes in series or by single-two spelling. Page 18 4 349 92 6. Application scope of patent. The above-mentioned second bias transistor is further connected in series with a diode and then coupled to the above voltage reference point. ^ 13. The device according to item 8 of the scope of patent application, wherein the third and fourth transistors of the third current source unit have the same size, and the third and fourth diodes have the same size size. 1 4. The device according to item 1 of the scope of patent application, wherein t, all the transistors mentioned above are empty FET transistors. 15. The device according to item 1 of the scope of patent application, wherein all the diodes mentioned above are high energy barrier diodes or Shottky diodes. 16. According to the device described in the first item of the scope of patent application, the second current source unit further couples the current flowing in the second current path in a current mirror manner as a fourth current source β. 17. The device according to item 16 of the scope of patent application, wherein the fourth current source is further connected in series with a resistor and a diode in order to convert the fourth current source into a voltage source. 18. The device according to item 1 of the scope of patent application, wherein the second current source unit further couples the current flowing in the second current path in a current mirror manner as a fifth current. And the third current source unit couples the current flowing in the third current path in a current mirror manner as a sixth current source; and then combines the fifth and sixth current sources Into a seventh current source. 1 9. A current source device having a temperature compensation function, comprising: a first current source unit for providing a first current having a constant current value; Page 19 VI. Patent application scope A second current source unit provides a second current whose current value increases with increasing temperature; wherein the second current source unit includes at least i a first transistor, a The first diode constitutes a first current path through which the second current flows; a second transistor and a second diode constitute a second current path through which the second current flows; the value of the second current depends on A size ratio between the first diode and the second diode; a third current source unit for providing a third current, the value of which is the difference between the first current and the second current: The first current source unit is connected in series with the second current source unit, and the third power source unit is connected in parallel with the third power source unit. 20. The device according to item 19 of the application, wherein the second current source unit further includes a biasing device for biasing the first transistor and the second transistor. 21. The device according to item 19 in the scope of patent application, wherein the first current source unit includes at least two current paths, respectively, through which the first current flows, and a first transistor connected in series to the second current unit. And a second transistor. 22. The device according to item 21 of the scope of patent application, wherein the current path in each of the first current source units is composed of a transistor connected in series with a diode, and the bias of the transistor is The voltage pole is coupled to the cathode of the diode. 23. The device according to item 19 of the scope of patent application, wherein the third current unit includes at least: a third transistor and a third diode, forming a third current path to flow the third current; A fourth transistor Page 20 6. The scope of patent application, a fourth diode, constitutes a fourth current path to flow the third current. 24. The device described in claim 23, wherein the third current source unit further includes a biasing device for biasing the third transistor and the fourth transistor. 25. The device according to item 23 of the scope of patent application, wherein the third and fourth transistors of the third current source unit have the same size, and the third and fourth diodes have the same size . 26. The device described in item 19 of the scope of the patent application, further comprises the second current source unit coupling the current flowing in the second current path in a current mirror manner as a fourth current source. 27. The device according to item 26 of the scope of the patent application, wherein the fourth current source is further connected in series with a resistor and a diode in order to convert the fourth current source into an electric dust source. 28. The device according to item 19 of the scope of patent application, wherein the second current source unit further couples the current flowing in the second current path in a current mirror manner as a fifth current. And the third current source unit A couples the current flowing in the third current path in a current mirror manner as a sixth current source; and then combines the fifth and sixth current sources Into a seventh current source. Page 21