Patent Application
20130099769
1. Field of Invention
The present invention relates to a current source circuit and a current source system, and more particularly to a current source circuit with high order temperature compensation and having a simple structure, and a current source system thereof.
2. Description of Related Arts
A bandgap reference circuit utilizes a sum of a voltage in proportion to the temperature and a diode drop, wherein temperature coefficients of the voltage and the diode drop are canceled out, in such a manner that a reference voltage independent of the temperature is achieved. The reference voltage thereof is similar to a bandgap of silicon, so the reference voltage is called bandgap reference. A current source circuit adopts a bandgap reference circuit to generate a current source, which causes a big area and a complex structure thereof, and increases a cost of a chip thereof. Moreover, the current source generated by the bandgap reference circuit changes greatly with changing of the temperature.
In view of the descriptions mentioned above, it is necessary to provide a current source circuit with high order temperature compensation and having a simple structure, and a current source system thereof.
A current source circuit with high order temperature compensation, comprises a reference voltage terminal, a first power module connected with the reference voltage terminal, a second power module connected with the reference voltage terminal, a control module connected with the second power module, a current source output module connected with the first power module and the control module, and a bias current source module connected with the second power module, the control module and the current source output module, wherein the control module comprises a first field effect tube (FET), a second FET connected with the first FET, and a third FET connected with the second FET; the bias current source module comprises a first bias current source connected with the second FET, and a second bias current source connected with the third FET; the current source output module comprises a fourth FET connected with the third FET and the second bias current source, a fifth FET connected with the fourth FET, and an output terminal connected with the fifth FET; the first power module comprises a first comparator connected with the reference voltage terminal, a sixth FET connected with the first comparator and the fourth FET, a first resistor connected with the sixth FET, and a second resistor connected with the first resistor; the second power module comprises a second comparator connected with the reference voltage terminal, a seventh FET connected with the second comparator, the first FET and the second bias current source, a third resistor connected with the seventh FET, and a fourth resistor connected with the third resistor.
A current source system with high order temperature compensation, comprises a reference voltage terminal, a first power module connected with the reference voltage terminal, a second power module connected with the reference voltage terminal, a control module connected with the second power module for providing the current source system with a temperature compensation, a current source output module connected with the first power module and the control module for generating a current source, and a bias current source module connected with the second power module, the control module, and the current source output module for providing the current source with an operating current required.
Compared with the prior art, the current source circuit with high order temperature compensation and current source system thereof according to preferred embodiments of the present invention are capable of generating a current source having a high-temperature characteristic without adopting of a bandgap reference circuit, have simple structures, and are easy to implement.
These and other objectives, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.
Referring to
Further referring to
The reference voltage terminal is for inputting a reference voltage VREF to the first power module and the second power module; the first power module is for providing the current source output module with a voltage VC1 having a first order positive temperature characteristic; the second power module is for providing the control module with a voltage VC2 having a first order positive temperature characteristic; the control module is for providing temperature compensation to the current source system having high order temperature compensation, in such a manner that a current source generated hardly changes with the temperature; the bias current source module is for supplying an operating current required to the current source system with high order temperature compensation; and the current source output module is for generating the current source.
According to the preferred embodiment of the present invention, connections of the current source circuit with high order temperature compensation are as follows. Both an inverting input terminal of the first comparator CMP1 and an inverting terminal of the second comparator CMP2 are connected with the reference voltage terminal, so as to receive the reference voltage VREF input by the reference voltage terminal. A non-inverting terminal of the first comparator CMP1 is connected with both a first terminal of the first resistor R1 and a first terminal of the second resistor R2, a non-inverting terminal of the second comparator CMP2 is connected with a first terminal of the third resistor R3 and a first terminal of the fourth resistor R4. A gate electrode of the sixth FET M6 is connected with an output terminal of the first comparator CMP1, a gate electrode of the seventh FET M7 is connected with an output terminal of the second comparator CMP2. A source electrode of the sixth FET M6 is connected with a source electrode of the seventh FET M7 and a power terminal VCC, a drain electrode of the sixth FET M6 is connected with a second terminal of the first resistor R1 and a source electrode of the fourth FET M4, a drain electrode of the seventh FET M7 is connected with a second terminal of the third resistor R3, a gate electrode of the first FET M1, a source electrode of the first FET M1, and a first terminal of the second bias current source 12. A gate electrode of the second FET M2, a source electrode of the second FET M2, and a gate electrode of the third FET M3 are all connected with a drain electrode of the first FET M1, a drain electrode of the second FET M2 is connected with a first terminal of the first bias current source I1. A source electrode of the third FET M3 is connected with a second terminal of the second bias current source I2 and a gate electrode of the fourth FET M4, a drain electrode of the fourth FET M4, a gate electrode of the fifth FET M5, and a drain electrode of the fifth FET M5 are all connected with the output terminal Vout. A second terminal of the first bias current source I1, a drain electrode of the third FET M3, a source electrode of the fifth FET M5, a second terminal of the second resistor R2 and a second terminal of the fourth resistor R4 are all connected with a ground terminal GND
Working principles of the current source circuit with high order temperature compensation and the current source system thereof according to preferred embodiments of the present invention are as follows.
Firstly, the first FET M1, the second FET M2, and the third FET are set to be equal in length and width, and a channel length L of the fourth FET M4 is equal to channel lengths of the first FET M1, the second FET M2, and the third FET M3, so as to ensure that the first FET M1, the second FET M2, the third FET M3, and the fourth FET M4 all have an equal threshold voltage.
It is known from a circuit diagram shown in
V1=VC2−VGS1−VGS2;
V2=V1+VGS3=VC2−VGS1−VGS2+VGS3;
further because
VGS1=VTH+(2*I11*K1/(W/L)1)0.5;
VGS2=VTH+(2*I22*K1/(W/L)2)0.5; and
VGS3=VTH+(2*I33*K1/(W/L)3)0.5;
wherein VGS1, VGS2, and VGS3 are respectively gate-source voltages of the first FET M1, the second FET M2, and the third FET M3, K1 is a process constant, K1=μn*Cox,μn is an electron mobility, Cox is a gate oxide thickness of an FET process, VTH is a threshold voltage of an FET, I11, I22 and I33 are respectively currents that flow through the first FET M1, the second FET M2 and the third FET M3, (W/L)1, (W/L)2, and (W/L)3 are respectively breadth length ratios of the first FET M1, the second FET M2 and the third FET M3,
it is obtained that:
V2=VC2−(VTH+(2*I11*K1/(W/L)1)0.5−(VTH+(2*I22*K1/(W/L)2)0.5)+(VTH+(2*I33*K1/(W/L)3)0.5);
wherein I11=I22=I1=I,I33=I2=4I, (W/L)1=(W/L)2=(W/L)3,
so
V2=VC2−VTH;
accordingly, a gate-source voltage of the fourth FET M4 is VGS4, VGS4=VC1−VC2+VTH;
it is set that VC1>VC2, and VREF=aT+b, wherein both a and b are constants, i.e., the reference voltage VREF is linear with the temperature T, so:
VC1=VREF*(R1+R2)/R2=(aT+b)*(R1+R2)/R2; and
VC2=VREF*(R3+R4)/R4=(aT+b)*(R3+R4)/R4;
so the fourth FET M4 is working in a saturation region, and a current that flows through the fourth FET M4 is I44,
if (R1+R2)/R2=α, (R3+R4)/R4=β, wherein both α and β are proportional coefficients,
VC1−VC2=(aT+b)*(α−β) (2),
putting the equation (2) into the equation (1), it is obtained that:
I44=μn*Cox*(W/L)4*(aT+b)2*(α−β)2/2;
a derivative of I44 is calculated with respect to T, it is obtained that:
∂I44/∂T=μ0*Cox*(W/L)4*T−5/2(α−β)2*(aT+b)*(aT−3b)/4.
It is known from the above equation that a value thereof is very small, i.e., a temperature coefficient of a current generated by the current source circuit with high order temperature compensation or the current system thereof is very small.
The current that flows through the fourth FET M4 is the current source generated by the current source circuit and system with high order temperature compensation according to a preferred embodiment of the present invention, so structures of the current source circuit and system according to preferred embodiments of the present invention provide high order temperature compensation for the current source output.
The current source circuit with high order temperature compensation and the current source system thereof according to preferred embodiments of the present invention are capable of generating a current source having a low temperature coefficient. It is verified that a variation of the current output thereby is approximately 3% in a full temperature range from −40° C. to 125° C. It can be seen from the descriptions mentioned above that the current source circuit with high order temperature compensation and the current source system thereof according to preferred embodiments of the present invention are capable of generating a high-temperature characteristic current source without a bandgap reference circuit, have simple structures and are easy to control.
One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting.
It will thus be seen that the objects of the present invention have been fully and effectively accomplished. Its embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201110317652.4 | Oct 2011 | CN | national |
