Current mirror and light emitting device with the current mirror

Current mirror and light emitting device using the same

This creation relates to a current mirror, and particularly to a current mirror that provides a large current.

Figure 1 shows the drain-source voltage V of an n-type metal-oxide-semiconductor (NMOS) transistor._DSGate source voltage V_GS, And drain current i_DThe relationship between. V_tIs the threshold voltage of the NMOS transistor. When V_DS&lt;V_GS-V_tWhen the NMOS transistor is located in a triode region,<img file="TWM302832U_D0001.tif" />. When V_DS&gt; V_GS-V_tWhen the NMOS transistor is in a saturation region,<img file="TWM302832U_D0002.tif" />. According to the above formula, the gate-source voltage V_GSThe larger the drain current i_DBigger.

FIG. 2 is a conventional current mirror 200 including two NMOS transistors 202 and 204. Transistors 202 and 204 have the same gate-source voltage V_GS, The channel area width-to-length (W / L) ratio is 1: N, and has the same μ_n, C_ox. The drain and the gate of the transistor 202 are connected together, so the transistor 202 operates in a saturation region. To make the load current 206_LN times the drain current of transistor 202 (I_L= NI), the transistor 204 must also operate in the saturation region. Drain-source voltage V of transistor 204_DSIt should not be too large, so as not to limit the pressure drop that the load 206 can use. Refer to Figure 1 for low V_DSOperating in the saturation region, the gate-source voltage V_GSMust be very low, at which time the current value will be small. Therefore, in the conventional current mirror 200, in order to provide a large current to the load 206, the demand for providing a large current to the load can only be achieved by increasing the size of the transistor 204 (increase N), but this method does not meet the current reduction Wafer volume trends. Therefore, we need a new current mirror that can provide a large current without using an excessively large transistor size and maintain the usable range of the voltage drop of the load.

This creation provides a current mirror that provides a large current without the need for an excessively large transistor size and maintains a usable range of load voltage drop. The current mirror includes an input stage circuit, an output stage circuit, a first operational amplifier, a control circuit, and a second operational amplifier. The input stage circuit includes a first transistor. The current flowing through the first transistor is an input current. The output stage circuit includes a second transistor. The second transistor has the same gate-source voltage as the first transistor. The current flowing through the second transistor is an output current. There is a fixed ratio between the output current and the input current. The first operational amplifier generates an output signal according to the drain-source voltage of the first transistor and the second transistor. According to the output signal, the control circuit adjusts the drain-source voltage of the second transistor so that the drain-source voltage of the first transistor and the second transistor are equal. According to a control voltage and a drain-source voltage of the first transistor, the second operational amplifier controls the first transistor so that the drain-source voltage of the first transistor is equal to the control voltage. The first and second transistors can be operated in the triode region by setting the control voltage.

The control circuit includes a third transistor. The gate of the third transistor is coupled to the output of the first operational amplifier, and the source is coupled to the inverting input of the first operational amplifier and the drain and drain of the second transistor. end. The load terminal can be coupled to a load. The current flowing through the load is the output current. The gate of the first transistor is coupled to the output terminal of the second operational amplifier, and the drain is coupled to the non-inverting input terminal of the second operational amplifier. The fixed ratio can be determined by adjusting the width-to-length ratio of the channel region of the first transistor and the second transistor. The transistors may be all NMOS transistors or all PMOS transistors.

The load may also be a plurality of light emitting diodes connected in series. Since the second transistor can be operated in the triode region, the drain voltage drop of the second transistor is sufficiently small, and the load end of the current mirror can be connected in series with more light-emitting diodes.

FIG. 3 is a current mirror 300 provided in this application, which includes an input stage circuit 302, an output stage circuit 304, a first operational amplifier 306, a control circuit 308, and a second operational amplifier 310. The input stage circuit 302 includes a first NMOS transistor M_n1. Flow through the first NMOS transistor M_n1The current is an input current I. Output stage circuit 304 includes a second NMOS transistor M_n2. While flowing through the second transistor M_n2The current is an output current I_L. Among them, the output current I_LThere is a fixed ratio N to the input current I. First NMOS transistor M_n1The gate is coupled to the output terminal of the second operational amplifier 310, and the drain is coupled to the non-inverting input terminal of the second operational amplifier 310. First NMOS transistor M_n1With the second NMOS transistor M_n2Have the same gate-source voltage V_GS, And has a channel length aspect ratio of 1: N. According to the first and second NMOS transistors M_n1With M_n2Drain-source voltage V_DS1With V_DS2The first operational amplifier 306 generates an output signal 312. The control circuit 308 adjusts the second NMOS transistor M according to the output signal 312_n2Drain-source voltage V_DS2To make the first and second NMOS transistors M_n1With M_n2Drain-source voltage V_DS1With V_DS2equal. In FIG. 3, the control circuit 308 includes a third NMOS transistor M_n3. Third NMOS transistor M_n3The gate is coupled to the output of the first operational amplifier 306, the source is coupled to the inverting input of the first operational amplifier 306 and the second transistor M_n2The drain terminal and the drain terminal are the load terminals of the current mirror 300. The load terminal can be coupled to a load 314. The current flowing through the load 314 is the output current I_L. According to a control voltage V_cAnd the first NMOS transistor M_n1Drain-source voltage V_DS1The second operational amplifier 310 controls the first NMOS transistor M_n1To make the first NMOS transistor M_n1Drain-source voltage V_DS1Equal to the control voltage V_c。

Since the current mirror 300 will be V_DS1With V_DS2Are controlled at the control voltage V_cAnd the first and second transistors M_n1With M_n2Have the same gate-source voltage V_GS, So by adjusting the control voltage V_c, The first and second transistors M_n1With M_n2Operates in the triode region, where<maths><img file="TWM302832U_D0003.tif" /></maths>

Control voltage at this time V_cIt is small, so the load 314 has a large usable voltage drop. And the first and second transistors M_n1With M_n2Gate source voltage V_GSIt is not necessary to be limited to a low voltage value like the conventional current mirror 200, so when the input current I is large, the first and second transistors M_n1With M_n2Will automatically increase the gate-source voltage V_GSWithout the need to expand the transistor size. Therefore, the current mirror 300 can provide a large current to the load 314 with an appropriate transistor size, and the load 314 can have a sufficient voltage drop.

The current mirror 400 in FIG. 4 is another embodiment of the present invention. The transistors used therein are all PMOS transistors. The remaining technical features are the same as those of the current mirror 300.

FIG. 5 is a light emitting device 500, which is an embodiment of the present invention. The light-emitting device 500 includes a current mirror 300 shown in FIG. 3 and a load 502. The load 502 is formed by connecting a plurality of light emitting diodes (LEDs) in series. Since the voltage of the load terminal 504 of the current mirror 300 is very low, a plurality of light emitting diodes can be connected in series. The current mirror 400 can also be used to implement the light-emitting device proposed in this creation.

A chip usually has a plurality of output stage circuits coupled to the same input stage circuit. If the distance between the output stage circuit and the input stage circuit is too far, a gradient effect will occur. In this case, the gate-source voltage of the transistor of the output stage and the input stage will have an error and cannot be exactly equal. The transistor provided in this work can be operated at a large gate-source voltage without increasing the size of the transistor. Compared to the traditional current mirror 200, the gradient effect is greatly improved in the current mirror of this work. In addition, the error of the output current of each output stage will be smaller.

The above implementations are only used to help understand this creation, not to limit the scope of this creation. Any product or technology developed based on the scope of the patent application for this creation belongs to the scope of protection of this specification.

<p>200 traditional current mirror</p><p>202,204NMOS transistor</p><p>206Load</p><p>300Current Mirror</p><p>302input stage circuit</p><p>304Output stage circuit</p><p>306The first operational amplifier</p><p>308Control circuit</p><p>310Second Operational Amplifier</p><p>312output signal</p><p>400current mirror</p><p>502, 314 load</p><p>504Load side</p><p>IInput current</p><p>I_LOutput current</p><p>V_cControl voltage</p><p>M_n1, M_n2, M_n3The first, second and third NMOS transistors</p><p>V_DDpower supply</p><p>V_DS1, V_DS2Drain source voltage</p><p>V_GS Gate-source voltage</p>

Figure 1 shows the drain-source voltage V of an n-type metal-oxide-semiconductor (NMOS) transistor._DSGate source voltage V_GS, And drain current i_DFigure 2 is a traditional current mirror; Figure 3 is an embodiment of the current mirror of the creation; Figure 4 is another embodiment of the current mirror of the creation; An embodiment of a light emitting device.