Patent Application
20150237691
This application claims priority to Chinese Patent Application No. 201110224941.X, filed Aug. 4, 2011, commonly assigned, incorporated by reference herein for all purposes.
The present invention is directed to integrated circuits. More particularly, the invention provides systems and methods for current matching. Merely by way of example, the invention has been applied to current matching of LED channels. But it would be recognized that the invention has a much broader range of applicability.
Liquid crystal displays (LCDs) have been widely used in various electronics products. A LCD panel usually does not have a self-illuminating property. A backlighting source often needs to be used to illuminate the LCD panel from the back of the LCD panel. Each pixel of the LCD panel often filters the light from the backlighting source differently to produce images. Light emitting diodes (LEDs) have been used in backlighting for LCDs. When multiple channels of LEDs are implemented for backlighting, a reference current can be provided to generate channel currents for driving LEDs, and the error of the channel currents is usually no more than 2% in order to evenly backlight a LCD screen.
In addition, a current balancing structure 112 includes a channel reference generator 116, and channel drivers 1181, . . . , 118n. The channel reference generator 116 receives a reference current 120, and generates channel driving currents 1221, . . . , 122n. The channel driving currents 1221, . . . , 122n are received by the channel drivers 1181, . . . , 118n, respectively. Then the channel drivers 1181, . . . , 118n provide channel currents 1241, . . . , 124n to the LED channels 1021, . . . , 102n, respectively. The channel drivers 1181, . . . , 118n can have similar structures and perform similar operations.
The channel driver 200 receives a current signal 210 (e.g., the channel driving current 1221) which flows through the resistor 204 (e.g., the resistor 128). The operational amplifier 202 receives a voltage signal 212 at an input terminal 216, and in response generates an amplified signal 218. The amplified signal 218 is received by the transistor 208 which is also coupled to another input terminal 220 of the operational amplifier 202. As a result, the transistor 208 generates a channel current 222 (e.g., the channel current 1241) which flows through a LED channel (e.g., the LED channel 1021), the transistor 208 (e.g., the transistor 132), and the resistor 206 (e.g., the resistor 130).
As shown in
where Iout represents the channel current 222, K×R represents the resistance of the resistor 204, and Ich represents the current signal 210. Additionally, Vos represents an input offset of the operational amplifier 202, R represents the resistance of the resistor 206, K×R×Ich represents the voltage signal 212, and Vos/R represents an error term.
Referring to
For example, the voltage signal 212 is only about 100 mV or less. In contrast, the input offset (e.g., Vos) can be as large as 10 mV for the CMOS technology. Thus, it can be difficult to reduce the mismatching error of the channel currents of the different LED channels (e.g., the channel currents 1241, . . . , 124n) to less than or equal to 2%. In order to improve matching of the channel currents, one option is to use P-N-P BJTs in the operational amplifier 202. But, for such P-N-P BJTs, a lateral structure is often required, which can increase the manufacturing difficulty. Also, additional circuits may also be needed because the current gain (e.g., β) of a P-N-P BJT usually is lower than an N-P-N BJT.
Hence it is highly desirable to improve techniques of current matching of LED channels.
The present invention is directed to integrated circuits. More particularly, the invention provides systems and methods for current matching. Merely by way of example, the invention has been applied to current matching of LED channels. But it would be recognized that the invention has a much broader range of applicability.
According to one embodiment, a system for generating a plurality of channel currents includes a channel reference generator, a first channel current divider, a second channel current divider, a first channel driver, and a second channel driver. The channel reference generator is configured to receive a first reference current and generate at least a first channel driving current and a second channel driving current. The first channel current divider is configured to receive the first channel driving current and generate a first input current, a second input current, and a third input current. The second channel current divider is configured to receive the second channel driving current and generate a fourth input current, a fifth input current, and a sixth input current. The first channel driver is configured to receive the first input current, the second input current, and the third input current and generate a first channel current. The second channel driver is configured to receive the fourth input current, the fifth input current, and the sixth input current and generate a second channel current. Moreover, a sum of the first input current and the second input current is equal to the first channel driving current. The second input current is equal to the third input current. A sum of the fourth input current and the fifth input current is equal to the second channel driving current. Furthermore, the fifth input current is equal to the sixth input current.
According to another embodiment, a system for generating a plurality of channel currents includes a channel reference generator, a first channel current divider, a second channel current divider, a first channel driver, and a second channel driver. The channel reference generator is configured to receive a first reference current and generate at least a first channel driving current and a second channel driving current. The first channel current divider is configured to receive the first channel driving current and generate a first input current, a second input current, and a third input current. The second channel current divider is configured to receive the second channel driving current and generate a fourth input current, a fifth input current, and a sixth input current. The first channel driver is configured to receive the first input current, the second input current, and the third input current and generate a first channel current. The second channel driver is configured to receive the fourth input current, the fifth input current, and the sixth input current and generate a second channel current. Furthermore, the first channel driver includes a first transistor including a first transistor terminal, a second transistor terminal, and a third transistor terminal, a second transistor including a fourth transistor terminal, a fifth transistor terminal, and a sixth transistor terminal, a first resistor associated with a first resistance and coupled to the third transistor terminal at a first voltage, and a second resistor associated with a second resistance and coupled to the sixth transistor terminal at a second voltage. Additionally, the first transistor terminal and the fourth transistor terminal are coupled. The second transistor terminal is configured to receive the second input current. The fifth transistor terminal is configured to receive the third input current. Moreover, a multiplication of the first resistance and a sum of the second input current and the first channel current is equal to a first magnitude. A multiplication of the second resistance and a sum of the first input current and the third input current is equal to a second magnitude. The first magnitude is equal to the second magnitude minus an offset voltage. The offset voltage is equal to a difference between the second voltage and the first voltage in magnitude.
According to yet another embodiment, a method for generating a plurality of channel currents includes receiving a first reference current, generating at least a first channel driving current and a second channel driving current, and processing information associated with the first channel driving current and the second channel driving current. Further, the method includes generating a first input current, a second input current, and a third input current based on at least information associated with the first channel driving current, processing information associated with the first input current, the second input current, and the third input current, generating a fourth input current, a fifth input current, and a sixth input current based on at least information associated with the second channel driving current, and processing information associated with the fourth input current, the fifth input current, and the sixth input current. Additionally, the method includes generating a first channel current based on at least information associated with the first input current, the second input current, and the third input current, and generating a second channel current based on at least information associated with the fourth input current, the fifth input current, and the sixth input current. Moreover, a sum of the first input current and the second input current is equal to the first channel driving current. The second input current is equal to the third input current. A sum of the fourth input current and the fifth input current is equal to the second channel driving current. The fifth input current is equal to the sixth input current.
According to yet another embodiment, a method for generating a plurality of channel currents includes receiving a first reference current, generating at least a first channel driving current and a second channel driving current, and processing information associated with the first channel driving current and the second channel driving current. The method further includes generating a first input current, a second input current, and a third input current based on at least information associated with the first channel driving current, processing information associated with the first input current, the second input current, and the third input current, generating a fourth input current, a fifth input current, and a sixth input current based on at least information associated with the second channel driving current, and processing information associated with the fourth input current, the fifth input current, and the sixth input current. Furthermore, the method includes generating a first channel current based on at least information associated with the first input current, the second input current, and the third input current, and generating a second channel current based on at least information associated with the fourth input current, the fifth input current, and the sixth input current. Moreover, a multiplication of a first resistance and a sum of the second input current and the first channel current is equal to a first magnitude. A multiplication of a second resistance and a sum of the first input current and the third input current is equal to a second magnitude. The first magnitude is equal to the second magnitude minus an offset voltage.
Depending upon embodiment, one or more benefits may be achieved. These benefits and various additional objects, features and advantages of the present invention can be fully appreciated with reference to the detailed description and accompanying drawings that follow.
The present invention is directed to integrated circuits. More particularly, the invention provides systems and methods for current matching. Merely by way of example, the invention has been applied to current matching of LED channels. But it would be recognized that the invention has a much broader range of applicability.
According to one embodiment, the channel reference generator 302 receives a reference current 308, and generates channel driving currents 3101, . . . , 310m, . . . , and 310n. For example, the channel driving currents are matched (e.g., within an error of no more than 1%). According to another embodiment, the channel current dividers 3041, . . . , 304m, . . . , and 304n receive the channel driving currents 3101, . . . , 310m, . . . , and 310n, respectively. In response to the received channel driving currents, the channel current dividers 3041, . . . , 304m, . . . , and 304n generates input currents (e.g., 3121, . . . , 312m, . . . , 312n, 3141, . . . , 314m, . . . , 314n, 3161, . . . , 316m, . . . , 316n) for the LED channel drivers 3061, . . . , 306m, . . . , and 306n, respectively. For example, the channel current divider 304m receives the channel driving current 310m, and in response generates three input currents 312m, 314m, and 316m, which are received by the LED channel driver 306m.
In another example, the input current 314m is proportional to the current 316m by a predetermined ratio (e.g., the predetermined ratio being equal to 1). In yet another example, the channel driving current 310m is proportional to the sum of the current 316m and the current 312m by a predetermined ratio (e.g., the predetermined ratio being equal to 1). In yet another example,
I
ch
=I
in
+I
2 (Equation 2)
and I1=I2 (Equation 3)
wherein Ich represents the channel driving current 310m. Additionally, Iin represents the input currents 312m, I1 represents the input current 314m, and I2 represents the input current 316m.
According to yet another embodiment, the LED channel drivers 3061, . . . , 306m, . . . , and 306n, receive the input currents from the channel current dividers 3041, . . . , 304m, . . . , and 304n, respectively. In response, the LED channel drivers 3061, . . . , 306m, . . . , and 306n generate channel currents 3181, . . . , 318m, . . . , and 318n respectively. According to yet another embodiment, the channel currents 3181, . . . , 318m, . . . , and 318n flow through output terminals 3201, . . . , 320n, . . . , and 320n, respectively, for driving corresponding LED channels.
For example, the transistors 402 and 404, and the transistors 4061, . . . , 406m, . . . , and 406n are n-channel field effect transistors (FETs). In another example, the transistors 410 and 412, and the transistors 4081, . . . , 408m, . . . , and 408n are N-P-N BJTs. In yet another example, the transistors 402, 404, 410 and 412, and the resistors 414, 416 and 420 form a current mirror circuit. In yet another example, the resistors 414 and 416, and the resistors 4181, . . . , 418m, . . . , and 418n all have the same resistance.
According to one embodiment, the channel reference generator 302 receives the reference current 308 which flows through the transistors 402 and 410. For example, the reference current 308 is mirrored, with a predetermined ratio, to generate a current 403 that flows through the transistors 404 and 412. In another example, the transistor 402 includes a gate terminal, which outputs a gate voltage signal 405 to the transistor 404 and the transistors 4061, . . . , 406m, . . . , and 406n. Additionally, the transistors 4081, . . . , 408m, . . . , and 408n each receive a base current 411 from the base terminal of the transistor 412.
As shown in
According to yet another embodiment, the transistors 522, 524, 526, 528, 530 and 532 form a first current mirror circuit. For example, in the first current mirror circuit, the transistors 524 and 530 form a first circuit branch, the transistors 522 and 528 form a second circuit branch, and the transistors 526 and 532 form a third circuit branch. In another example, the first circuit branch, the second circuit branch, and the third circuit branch are mutually coupled. According to yet another embodiment, the transistors 502, 504, 506 and 508 form a second current mirror circuit. For example, in the second current mirror circuit, the transistors 502 and 506 form a fourth circuit branch, and the transistors 504 and 508 form a fifth circuit branch. In another example, the fourth circuit branch and the fifth circuit branch are coupled. According to yet another embodiment, the transistors 510, 512, 514, 516, 518 and 520 form a third current mirror circuit. For example, in the third current mirror circuit, the transistors 510 and 516 form a sixth circuit branch, the transistors 512 and 518 form a seventh circuit branch, and the transistors 514 and 520 form an eighth circuit branch. In another example, the sixth circuit branch, the seventh circuit branch, and the eighth circuit branch are mutually coupled.
Referring to
According to yet another embodiment, the current 538 is generated by diverting at least a portion of a current 537 that is mirrored from the channel driving current 534 with a predetermined ratio. For example, the channel driving current 534 is proportional to the sum of the current 538 and the current 544 by a predetermined ratio (e.g., the predetermined ratio being equal to 1). In another embodiment, the currents 544 and 546 each are generated by mirroring a reference current 536 with a predetermined ratio. For example, the current 544 is proportional to the current 546 by a predetermined ratio (e.g., the predetermined ratio being equal to 1). In yet another example, the channel driving current 534, and the currents 538, 544 and 546 follow Equations 2 and 3, wherein Ich represents the channel driving current 534, Iin represents the current 538, I1 represents the current 546, and I2 represents the current 544.
In another embodiment, the channel current divider 500 receives the channel driving current 534 (e.g., the channel driving current 310m) from a channel reference generator (e.g., the channel reference generator 302). For example, the channel driving current 534 flows through the transistors 502 and 506, and is mirrored, with a predetermined ratio, by the transistor 504 to generate the current 537. In another example, the current 537 flows through the transistors 504 and is divided into currents 538 and 539. In another embodiment, the current 538 is sent, as an input current (e.g., the current 312m), to a LED channel driver (e.g., the LED channel driver 306m) as shown in
As shown in
According to another embodiment, the reference current 536 is also mirrored by the transistor 532 to generate a current 542, which is further mirrored by the transistor 512 to generate the current 544 and is also further mirrored by the transistor 514 to generate the current 546. For example, the current 544 flows through the transistors 512 and 518, and the current 546 flows through the transistors 514 and 520. In another example, the currents 544 and 546 are sent, as input currents (e.g., the currents 316m and 314m respectively) to a LED channel driver (e.g., the LED channel driver 306m) as shown in
In one embodiment, the LED channel driver 600 receives, from a channel current divider (e.g., the channel current divider 304m and/or the channel current divider 500), three input currents 638, 640 and 642. For example, the input currents 638, 640 and 642 are the input currents 314m, 316m and 312m, respectively. In another example, the input currents 638, 640 and 642 are the input currents 546, 544 and 538, respectively.
In response, the transistor 622 outputs a voltage signal 656 to the transistor 602 (e.g., through a terminal 658) according to one embodiment. For example, the transistor 602 receives the voltage signal 656 and generates a channel current 644 for driving a channel of one or more LEDs 632. In another example, the channel current 644 flows from the one or more LEDs 632 to the transistor 602 through a terminal 630 (e.g., the terminal 320m).
In one embodiment, the base of the transistor 614 and the base of the transistor 616 are coupled together. For example, the transistor 614 receives the input current 640, and the transistor 616 receives the input current 638. In another example, the input currents 638 and 640 are equal in magnitude. In another embodiment, the transistors 614 and 616 are coupled to the terminals 634 and 636 respectively. For example, the voltage difference between the terminals 634 and 636 are determined as follows:
where ΔV represents the voltage between terminals 634 and 636, and VT represents a thermal voltage. Additionally, Ic1 represents the input current 640, Ic2 represents the input current 638, and Is1 and Is2 represent reverse saturation currents of the transistors 614 and 616, respectively. For example, by adjusting device sizes and layout patterns, Ic1 (e.g., the input current 640) and Ic2 (e.g., the input current 638) can be matched (e.g., within an error of no more than 2%), and Is1 and Is2 can also be matched (e.g., within an error of no more than 1%). At room temperature, VT equals about 26 mV; hence ΔV (e.g., the voltage difference between terminals 634 and 636) can be reduced to about 1 mV according to one embodiment.
Referring back to
In yet another embodiment, the transistor 622 draws a base current 653 from the input current 640. For example, the base current 653 is compensated by the transistors 608, 610, and 624. In another example, the transistor 610 outputs a current 654 to the transistor 624 as a base current. In yet another example, the current 654 is mirrored by the transistor 608, with a predetermined ratio, to generate a current to compensate for the base current 653 in order to reduce the matching error of the input currents 638 and 640.
According to some embodiments, even though the currents 646 and 653 are small in magnitude (e.g., in the order of nano-amps), these currents 646 and 653 are diverted from the input currents 638 and 640 respectively. Hence, the compensation for the loss of these diverted currents can reduce the matching error of the input currents 638 and 640 and thus reduce the voltage difference between the terminals 634 and 636 for better channel current matching according to certain embodiments.
For example, the channel current 644 is determined as follows:
(Iin+I2)×K×R−Vos=(Iout+I1)×R (Equation 5)
where Iin represents the input current 642, I1 represents the input current 638, I2 represents the input current 640, and Iout represents the channel current 644. Additionally, K×R represents the resistance of the resistor 626, and R represents the resistance of the resistor 628. Moreover, Vos represents the voltage difference between the terminals 634 and 636.
In another example, if Iout is equal to 40 mA, R is equal to 5Ω, K is equal to 1000, and Iin is equals 16 μA, and if I1 and I2 each are equal to 4 μA, Equation 5 is simplified to the following form:
(Im+I2)×K×R−Vos=Iout×R (Equation 6).
In yet another example, using Equations 2 and 6, the channel current 644 can be determined as follows:
According to some embodiments, between different LED channel drivers, R and K×R each can be matched within an error of no more than 1%, through proper adjustment of device size and layout pattern. Additionally, for example, Vos is also reduced to no more than 1 mV, by matching the currents 640 and 638 (e.g., within an error of no more than 2%) and reducing the voltage difference between terminals 634 and 636 as shown in
According to another embodiment, a system for generating a plurality of channel currents includes a channel reference generator, a first channel current divider, a second channel current divider, a first channel driver, and a second channel driver. The channel reference generator is configured to receive a first reference current and generate at least a first channel driving current and a second channel driving current. The first channel current divider is configured to receive the first channel driving current and generate a first input current, a second input current, and a third input current. The second channel current divider is configured to receive the second channel driving current and generate a fourth input current, a fifth input current, and a sixth input current. The first channel driver is configured to receive the first input current, the second input current, and the third input current and generate a first channel current. The second channel driver is configured to receive the fourth input current, the fifth input current, and the sixth input current and generate a second channel current. Moreover, a sum of the first input current and the second input current is equal to the first channel driving current. The second input current is equal to the third input current. A sum of the fourth input current and the fifth input current is equal to the second channel driving current. Furthermore, the fifth input current is equal to the sixth input current. For example, the system is implemented according to
According to yet another embodiment, a system for generating a plurality of channel currents includes a channel reference generator, a first channel current divider, a second channel current divider, a first channel driver, and a second channel driver. The channel reference generator is configured to receive a first reference current and generate at least a first channel driving current and a second channel driving current. The first channel current divider is configured to receive the first channel driving current and generate a first input current, a second input current, and a third input current. The second channel current divider is configured to receive the second channel driving current and generate a fourth input current, a fifth input current, and a sixth input current. The first channel driver is configured to receive the first input current, the second input current, and the third input current and generate a first channel current. The second channel driver is configured to receive the fourth input current, the fifth input current, and the sixth input current and generate a second channel current. Furthermore, the first channel driver includes a first transistor including a first transistor terminal, a second transistor terminal, and a third transistor terminal, a second transistor including a fourth transistor terminal, a fifth transistor terminal, and a sixth transistor terminal, a first resistor associated with a first resistance and coupled to the third transistor terminal at a first voltage, and a second resistor associated with a second resistance and coupled to the sixth transistor terminal at a second voltage. Additionally, the first transistor terminal and the fourth transistor terminal are coupled. The second transistor terminal is configured to receive the second input current. The fifth transistor terminal is configured to receive the third input current. Moreover, a multiplication of the first resistance and a sum of the second input current and the first channel current is equal to a first magnitude. A multiplication of the second resistance and a sum of the first input current and the third input current is equal to a second magnitude. The first magnitude is equal to the second magnitude minus an offset voltage. The offset voltage is equal to a difference between the second voltage and the first voltage in magnitude. For example, the system is implemented according to
According to yet another embodiment, a method for generating a plurality of channel currents includes receiving a first reference current, generating at least a first channel driving current and a second channel driving current, and processing information associated with the first channel driving current and the second channel driving current. Further, the method includes generating a first input current, a second input current, and a third input current based on at least information associated with the first channel driving current, processing information associated with the first input current, the second input current, and the third input current, generating a fourth input current, a fifth input current, and a sixth input current based on at least information associated with the second channel driving current, and processing information associated with the fourth input current, the fifth input current, and the sixth input current. Additionally, the method includes generating a first channel current based on at least information associated with the first input current, the second input current, and the third input current, and generating a second channel current based on at least information associated with the fourth input current, the fifth input current, and the sixth input current. Moreover, a sum of the first input current and the second input current is equal to the first channel driving current. The second input current is equal to the third input current. A sum of the fourth input current and the fifth input current is equal to the second channel driving current. The fifth input current is equal to the sixth input current. For example, the method is implemented according to at least
According to yet another embodiment, a method for generating a plurality of channel currents includes receiving a first reference current, generating at least a first channel driving current and a second channel driving current, and processing information associated with the first channel driving current and the second channel driving current. The method further includes generating a first input current, a second input current, and a third input current based on at least information associated with the first channel driving current, processing information associated with the first input current, the second input current, and the third input current, generating a fourth input current, a fifth input current, and a sixth input current based on at least information associated with the second channel driving current, and processing information associated with the fourth input current, the fifth input current, and the sixth input current. Furthermore, the method includes generating a first channel current based on at least information associated with the first input current, the second input current, and the third input current, and generating a second channel current based on at least information associated with the fourth input current, the fifth input current, and the sixth input current. Moreover, a multiplication of a first resistance and a sum of the second input current and the first channel current is equal to a first magnitude. A multiplication of a second resistance and a sum of the first input current and the third input current is equal to a second magnitude. The first magnitude is equal to the second magnitude minus an offset voltage. For example, the method is implemented according to
For example, some or all components of various embodiments of the present invention each are, individually and/or in combination with at least another component, implemented using one or more software components, one or more hardware components, and/or one or more combinations of software and hardware components. In another example, some or all components of various embodiments of the present invention each are, individually and/or in combination with at least another component, implemented in one or more circuits, such as one or more analog circuits and/or one or more digital circuits. In yet another example, various embodiments and/or examples of the present invention can be combined.
Although specific embodiments of the present invention have been described, it will be understood by those of skill in the art that there are other embodiments that are equivalent to the described embodiments. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201110224941.X | Aug 2011 | CN | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13215000 | Aug 2011 | US |
| Child | 14632920 | US |
