CN113851075A - Constant current source driving module of LED display screen and control method thereof - Google Patents
Constant current source driving module of LED display screen and control method thereof Download PDFInfo
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- G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
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Abstract
The invention relates to an LED display screen constant current source driving module and a control method thereof, comprising an REXT loop module for clamping the voltage at two ends of an external resistor R _ EXT to a first voltage; the current detection module is connected with the first current mirror and used for detecting the output current of the first current mirror and outputting mirror image proportion control instructions of the first current mirror and the second current mirror; the first current mirror and the second current mirror perform mirror proportion adjustment according to the control instruction, so that the output current I1 of the first current mirror fluctuates within a fixed range, the segmented output of the constant current source is realized, the precision of the current mirror cannot change greatly along with the change of the output constant current, and the improvement of the precision of the constant current output is facilitated.
Description
Technical Field
The invention relates to the field of constant current sources, in particular to a constant current source driving module of an LED display screen and a control method thereof.
Background
Fig. 1 is a constant current source driving generation circuit in a common-anode LED display screen constant current source driving chip, and R _ EXT in fig. 1 is an external resistor of the driving chip.
Assuming that the gain of all amplifiers in fig. 1 is infinite, the constant current source is generated by the following principle:
generating a required reference potential VREF1 from Bandgap;
the source terminal potential of NM0 is clamped to VREF1 by amplifier AMP1, so the source-drain current flowing through PM0 is: i0 ═ VREF1/R _ EXT;
the PM1 and the PM0 are current mirrors, and the current ratio of the current mirrors (the source-drain current of the PM1 is greater than that of the PM 0) is K, so that the magnitude of the source-drain current of the PM1 is I1 ═ K × VREF1/R _ EXT;
when the constant current source channels are started, the amplifiers AMP3 and AMP _ C clamp the drain end potentials of NM1 and NM _ C0 to VREF2 respectively, the potentials of all ports of NM _ C0 of the constant current source output channels are the same as the potentials of all ports of NM1, the output current of the channels is proportional mirror image of the magnitude of NM1 source-drain current, the mirror image proportion is J, and then the magnitude (absolute value) of the output constant current of the constant current source channels at the moment is IOUT (J) K VREF/R _ EXT.
In a general constant current source driving chip, J × K is a fixed value, so the magnitude of the output constant current of the constant current source channel is generally determined by the magnitude of the external resistor R _ EXT.
The output constant current range of the constant current channel of a general constant current source driving chip is relatively wide (for most chips in the market, the minimum output value is more than 10 times the maximum output value), the current variation at this time is adjusted by R _ EXT, then the variation of I0, I1 and IOUT above is more than 10 times, the parameters of PM0, PM1, NM1 and NM _ C0 of each channel need to meet the requirement of normal operation under the maximum output current, then when the output current is minimum, PM0, PM1, NM1 and NM _ C0 of each channel have small | VGS | (the absolute value of VGS) so that the two sets of current mirrors mentioned above are deteriorated, and the precision of the output constant current source is also deteriorated.
In order to satisfy the range and precision of the constant current chip for outputting the constant current, the constant current driving chip generally performs the segmentation processing on the output current range:
in order to meet the accuracy of the minimum output current, it is necessary to increase W × L of PM0, PM1, NM1, and NM _ C0, that is, to increase the area of the above 4 devices, and the most effective method is to increase the length L;
due to the limitation of the power supply voltage VDD, | VGS | < VDD of PM0, PM1, NM1, and NM _ C0, if W/L of PM0, PM1, NM1, and NM _ C0 remains unchanged, the range of the output constant current is small. In order to increase the range of the output constant current, in the case of ensuring that all | VGS | are within a reasonable range, it is necessary to increase W/L (width-to-length ratio) of PM0, PM1, NM1, and NM _ C0 section by section, that is, to perform a segmentation process on the output current range.
The current I1 flowing through NM1 is inversely proportional to the magnitude of R _ EXT, and the drain voltage of NM1 is a fixed potential VREF2, and the gate voltage VG of NM1 increases as R _ EXT decreases. Therefore, it can be determined whether the chip operates in a correct current segment by detecting the gate voltage VG of NM 1. The voltage detection module compares the VG voltage with designed reference voltages VRB and VRT respectively, and the comparison result is output to the section selection control module. The section selection control module generates corresponding control signals according to the comparison result and controls the adjustment of the width-length ratios of the PM0, the PM1, the NM1 and the NM _ C0. When VRB < VG < VRT is detected, the width-to-length ratio of each MOS tube is not adjusted; when VG < VRB or VG > VRT is detected, the width-to-length ratio of each MOS tube is correspondingly adjusted.
Two common methods for adjusting the width-to-length ratio are provided:
keeping the width-to-length ratio of PM0 and PM1 constant, i.e. keeping the mirror ratio K of I1 to I0 constant, and keeping J × K constant, the mirror ratio J of IOUT to I1 remains constant. As the output current increases, the W/L of NM1 and NM _ C0 increases segment by segment, with the same ratio.
Keeping the width-to-length ratios of PM0 and NM1 unchanged, the W/L of NM _ C0 is increased section by section with the increase of the output current, and the mirror ratio J of IOUT and I1 is increased section by section. In order to keep J x K constant, the mirror ratio K of I1 to I0 needs to be reduced step by step, namely, the W/L of PM1 needs to be reduced step by step.
In order to meet the range and the precision of the output constant current, the design value of I1 in the two schemes is larger.
With method one, as the required IOUT current increases, I1 also increases proportionally, thus increasing the power consumption of the chip.
For the second method, the mirror ratio K is reduced section by section, and the power consumption is slightly reduced compared with the first method, but since the W/L of the PM1 is reduced section by section, the area of the PM1 is also reduced section by section, and the accuracy of the PM1 and the PM0 is reduced section by section. Moreover, the mirror ratio J, K needs to be changed simultaneously and J × K remains unchanged, which is not convenient for designing the width-to-length ratio of the MOS transistors of each current segment.
With both methods, since the width-to-length ratio of the PM0 is kept constant, as described above, the width-to-length ratio of the PM0 needs to satisfy the requirement of normal operation at the maximum output current, and then when the output current is minimum, the | VGS | (absolute value of VGS) of the PM0 and PM1 is small, the accuracy of the current mirror is degraded, and the accuracy of the output constant current source is also degraded.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides an LED display screen constant current source driving module and a control method thereof, which are used for realizing the sectional output of a constant current source, so that the precision of a current mirror cannot be greatly changed along with the change of the output constant current, and the improvement of the precision of the constant current output is facilitated.
The purpose of the invention is realized by the following technical scheme:
the utility model provides a LED display screen constant current source drive module, includes:
the REXT loop module is connected with the external resistor R _ EXT and used for clamping the voltage at two ends of the external resistor R _ EXT to a first voltage;
the REXT loop module comprises a first current mirror connected with the REXT loop module and one or more second current mirrors connected with the first current mirror, wherein an input channel of the first current mirror and an output channel of the second current mirror are formed by connecting a plurality of MOS (metal oxide semiconductor) tubes, so that the mirror ratio of the first current mirror and the second current mirror is adjustable;
the current detection module is connected with the first current mirror and is used for detecting the output current of the first current mirror and outputting mirror image proportion control instructions of the first current mirror and the second current mirror;
the first current mirror and the second current mirror perform mirror proportion adjustment according to the control instruction, so that the output current I1 of the first current mirror fluctuates within a fixed range.
For PMOS, operating in saturation, the current formula is as follows:
in the formula, mu, Cox、VTHCan be regarded as a constant, VOSPIs the offset voltage between PM0 and PM 1.
Because of the wide range of IOUT required, the IOUT maximum may be more than 10 times the IOUT minimum, while I0Proportional to IOUT, then I0Also more than 10 times. According to I0Is calculated according to the formula if
Remains unchanged, then VGSMay vary over a wide range. When IOUT is large, VGSIs also larger, VOSPThe proportion occupied in the current formula is small, and the current precision is high at the moment; when IOUT is small, VGSIs also smaller, VOSPThe current formula occupies a larger proportion, and the current precision is obviously reduced at the moment.
In order to satisfy the output range and precision of IOUT, the areas of PM0 and PM1 need to be made large to reduce the offset voltage VOSPAnd further decrease VOSPThe effect on current accuracy.
For NMOS, the current calculation formula is as follows
Similar to PMOS, when IOUT is larger, VGSIs also larger, VOSNThe proportion occupied in the current formula is small, and the current precision is high at the moment; when IOUT is small, VGSIs also smaller, VOSNThe proportion occupied in the current formula is large, and the current precision is reduced.
Furthermore, the second current mirror is connected with the first current mirror in sequence, or the second current mirror is respectively connected with the output channel of the first current mirror.
Furthermore, the input end of the REXT loop module is connected with a voltage control module, and the voltage control module is used for adjusting the input voltage of the REXT loop module to a second voltage.
Furthermore, the input end of the voltage control module is connected with a reference voltage source, and the reference voltage source is used for inputting a third voltage to the voltage control module.
Furthermore, the input end of the REXT loop module is connected with a reference voltage source, and the reference voltage source is used for inputting a third voltage to the REXT loop module.
Furthermore, the input channel of the first current mirror is formed by connecting a plurality of P-type MOS tubes, and a switching element is arranged in a connecting circuit of the first current mirror and used for controlling the access number of the MOS tubes.
Further, when the second current mirrors are connected with the first current mirror in sequence, the output channels of the odd second current mirrors are formed by connecting a plurality of N-type MOS (metal oxide semiconductor) tubes, and the output channels of the even second current mirrors are formed by connecting a plurality of P-type MOS tubes;
when the second current mirror is respectively connected with the output channel of the first current mirror, the output channel of the second current mirror is formed by connecting a plurality of N-type MOS tubes, and a connecting circuit of the second current mirror is provided with a switch element for controlling the access quantity of the MOS tubes.
Further, the MOS tube connection mode comprises parallel connection and series connection.
Further, the current detection module comprises a sampling circuit and a control module, the sampling circuit is connected with the first current mirror, the output current I0 of the first current mirror is sampled, the acquired sampling current is sent to the control module to be compared with the reference current mirror, when the sampling current is larger than the reference current, the mirror proportion of the first current mirror is reduced, and if the sampling current is smaller than the reference current, the mirror proportion of the first current mirror is increased until the sampling current is within the reference current threshold interval.
Further, the sampling circuit is an MOS transistor which forms an R _ EXT current mirror with an input channel of the first current mirror, and is configured to output a mirror current Icmp [ x ] of the first current mirror input current I0.
Further, the output channel of the R _ EXT current mirror is connected with a control module, and the reference current is set to [ IRB, IRT ], wherein IRB is the lower limit value of the reference current, and IRT is the upper limit value of the reference current;
the control module image current Icmp [ X ] is compared with reference current [ IRB, IRT ], and when Icmp [ X ] is not in the interval range of the reference current [ IRB, IRT ], the image proportion A [ X ] of the R _ EXT current mirror is adjusted until IRB is smaller than Icmp [ X ] < IRT;
meanwhile, the mirror ratio J [ X ] of the second current mirror is adjusted so that IOUT [ X ] is I1 × J [ X ], where I1 is the output circuit of the first current mirror.
Further, the control module includes:
the comparator is connected with an output channel of the R _ EXT current mirror and used for inputting a mirror current Icmp [ x ], and a reference end of the comparator inputs a reference current [ IRB, IRT ];
and the logic circuit is connected with the comparator and is used for outputting mirror ratio adjusting instructions of the first current mirror and the second current mirror so as to meet the following requirements:
when Icmp [ X ] is not in the interval range of the reference current [ IRB, IRT ], adjusting the mirror ratio A [ X ] of the R _ EXT current mirror until IRB < Icmp [ X ] < IRT;
meanwhile, the mirror ratio J [ X ] of the second current mirror is adjusted so that IOUT [ X ] is I1 × J [ X ].
Further, the adjusting instruction acts on the switching element and is used for controlling the number of the accessed MOS transistors, and the adjusting instruction includes:
a control signal SP [ M:1] with the width of M bits, which is used for controlling the mirror proportion KX of the first current mirror;
and a control signal SN [ N:1] with N bits of bit width for controlling the mirror ratio JX of the second current mirror;
m is the number of MOS (metal oxide semiconductor) tubes of the input channel of the first current mirror, and N is the number of MOS tubes of the output channel of the second current mirror.
Furthermore, the control signal of the regulating instruction is binary code, and each bit of binary number in the binary code corresponds to the control signal of one MOS tube;
wherein 0 represents on and 1 represents off;
or, 1 indicates on and 0 indicates off.
A constant current source driving control method of an LED display screen uses the LED display screen constant current source driving module, and the method comprises the following steps:
step S1: dividing the output current of the constant current source module into L sections;
step S2: the present constant current source module works in the section X current, the output current is IOUT [ X ], the mirror ratio of the first current mirror is KX, the mirror ratio of the second current mirror is J [ X ], the input current of the first current mirror is I0[ X ], then: IOUT [ X ] ═ I0[ X ] × J [ X ] × K [ X ];
step S3: when the constant current source module works at the (X + 1) th section of current, the voltage at the two ends of the external resistor R _ EXT is clamped to the first voltage through the REXT loop module, the input current of the first current mirror is I0 (X + 1), and the method comprises the following steps:
the output current is IOUT [ X +1] ═ I0[ X +1] × K [ X +1] × J [ X +1], and K [ X +1] ═ J [ X ] × K [ X ].
Further, when the output current of the constant current source module is sequentially increased from the 1 st section to the L th section, K [ X +1] < K [ X ], J [ X +1] > J [ X ], that is, when the output current is changed from IOUT [ X ] to IOUT [ X +1], the mirror ratio of the first current mirror is reduced, and the mirror ratio of the second current mirror is increased;
or;
when the output current of the constant current source module is reduced from the 1 st section to the L th section in sequence, K [ X +1] > K [ X ], J [ X +1] < J [ X ], that is, when the output current is changed from IOUT [ X ] to IOUT [ X +1], the mirror ratio of the first current mirror is increased, and the mirror ratio of the second current mirror is reduced.
Further, the method also comprises an output current section selection control method of the constant current source module, which comprises the following steps:
step S01: obtaining a mirror current Icmp [ x ] of the R _ EXT current mirror;
step S02: comparing the mirror current Icmp [ X ] with the reference current [ IRB, IRT ], and when the Icmp [ X ] is not in the interval range of the reference current [ IRB, IRT ], adjusting the mirror proportion A [ X ] of the R _ EXT current mirror until IRB is smaller than Icmp [ X ] < IRT;
wherein, IRB is the lower limit value of the reference current, and IRT is the upper limit value of the reference current.
Further, the specific step of step S02 is:
when the IRB < Icmp [ X ] < IRT is detected, the chip works in a state of a mirror image proportion A [ X ] of a current segment X and a mirror image proportion of an R _ EXT current mirror, namely the mirror image proportion of a first current mirror is KX;
when Icmp [ X ] < IRB is detected, the current segment of the chip work is changed from the Xth segment to the X-1 th segment, the mirror image proportion of the R _ EXT current mirror is changed from A [ X ] to A [ X-1], wherein A [ X-1] < A [ X ], the mirror image proportion of the first current mirror is changed from K [ X ] to K [ X-1], the mirror image current Icmp [ X ] is increased, and the next round of detection is carried out until IRB < Icmp [ X ] < IRT is detected;
when Icmp [ X ] IRT is detected, the current segment of the chip work is changed from the Xth segment to the X +1 th segment, the mirror ratio of the R _ EXT current mirror is changed from A [ X ] to A [ X +1], wherein A [ X ] is larger than A [ X +1], the mirror ratio of the first current mirror is changed from K [ X ] to K [ X +1], the mirror current Icmp [ X ] is reduced, and the next round of detection is carried out until IRB < Icmp < IRT is detected.
The invention has the beneficial effects that:
since the first current mirror output current I1 ═ K [ X ] × I0[ X ], IOUT [ X ] × K [ X ] × I0[ X ], I0 is inversely proportional to the magnitude of R _ EXT and J [ X ] × is a fixed constant, the output current IOUT is inversely proportional to the magnitude of R _ EXT in the full output current range. The K [ X ] is reduced section by section, the I1 can be changed in a smaller range as long as the current segmentation range is reasonably designed, the | VGS | (the absolute value of VGS) of each MOS tube in the current mirror is in a larger value, the precision of the current mirror cannot change greatly along with the change of the output constant current, and the improvement of the precision of the constant current output is facilitated. Under the condition of meeting the constant current output precision, the value of the current I1 can be designed to be small enough, which is beneficial to reducing the power consumption of the chip.
Drawings
FIG. 1 is a prior art schematic;
FIG. 2 is a schematic diagram of the present invention;
FIG. 3 is a schematic diagram of the connection of a first current mirror and a second current mirror;
FIG. 4 is an equivalent circuit of a current mirror;
FIG. 5 is an equivalent circuit of another current mirror
FIG. 6 is a first current mirror input channel circuit schematic;
FIG. 7 is a schematic diagram of a second current mirror output channel circuit
FIG. 8 is another schematic of the present invention
FIG. 9 is a circuit diagram of an example of the present invention;
FIG. 10 is a schematic diagram of a current sensing module.
Detailed Description
The technical solution of the present invention is further described in detail with reference to the following specific examples, but the scope of the present invention is not limited to the following.
Referring to fig. 2, an LED display screen constant current source driving module includes:
the REXT loop module is connected with the external resistor R _ EXT and used for clamping the voltage at two ends of the external resistor R _ EXT to a first voltage;
the REXT loop module comprises a first current mirror connected with the REXT loop module and one or more second current mirrors connected with the first current mirror, wherein an input channel of the first current mirror and an output channel of the second current mirror are formed by connecting a plurality of MOS (metal oxide semiconductor) tubes, so that the mirror ratio of the first current mirror and the second current mirror is adjustable;
the current detection module is connected with the first current mirror and is used for detecting the output current of the first current mirror and outputting mirror image proportion control instructions of the first current mirror and the second current mirror;
the first current mirror and the second current mirror perform mirror proportion adjustment according to the control instruction, so that the output current I1 of the first current mirror fluctuates within a fixed range.
Referring to fig. 2, which is an example of the present invention, a total of a first current mirror and a second current mirror is designed as a common-anode constant current driving chip, wherein the overall structure of the current mirror is not particularly limited.
As shown in fig. 4, it is a typical equivalent circuit of current mirror, which mainly has a MOS transistor M1And MOS transistor M2Composition, mirror currents are respectively I1And I2。
As shown in FIG. 5, the current mirror is a common-source common-gate current mirror, and comprises four MOS transistors M symmetrical to each other1-M4And (4) forming.
That is to say, what kind of form can be adopted for the current mirror in this scheme, and whatever current mirror type known in the art can be used in this scheme, the main improvement of this scheme lies in that the structure of the MOS transistor in the current mirror is improved, that is, the MOS transistor in the equivalent circuit can realize the adjustment of the width-to-length ratio (W/L), that is, the MOS transistor component referred to in this invention refers to the MOS transistor in the equivalent circuit, rather than a single MOS transistor, and the width-to-length ratio of the single MOS transistor has been determined in the manufacturing process, and obviously, it is impossible to adjust.
Optionally, in the LED display screen constant current source driving module, the second current mirror is sequentially connected to the first current mirror, or the second current mirror is respectively connected to the output channel of the first current mirror. For example, as shown in fig. 3, the second current mirror is connected to the first current mirror in sequence, and when a plurality of second current mirrors are present, the second current mirrors are connected in sequence, and finally an output channel is formed. Generally, the number of the second current mirrors is one or two, when two are used, the second current mirrors can be used as common cathode wiring, when one is used, the second current mirrors can be used as common anode wiring, as a special case, the second current mirrors can also be omitted, namely, only the output of the first current mirror is used as common cathode driving, and the scheme has internal consumption of a chip, so that the scheme is not in the discussion range of the scheme.
When the second current mirrors are respectively connected to the output channels of the first current mirror, each second current mirror is used as one output channel, which is equivalent to providing a plurality of output power supplies.
The input channel and the input channel referred to in the scheme are merely definitions of interfaces, and are not really limited to input or output, for example, referring to fig. 2, in a common-anode constant current source segmented module, two current mirrors are included, a first current mirror is composed of P-type MOS transistors, and both ports of the first current mirror are current flows, so that in terms of current direction, obviously both ports are output channels, but in the scheme, since the left side is connected with the input current I0, the left side is regarded as an input channel, that is, the input channel and the output channel in the present invention are not named in current direction, but are designed in connection relationship.
Optionally, an input end of the REXT loop module is connected to a voltage control module, and the voltage control module is configured to adjust an input voltage of the REXT loop module to a second voltage, as shown in fig. 8, that is, provide a second voltage to be input into the REXT loop module, so that the REXT loop module clamps voltages at two ends of an external resistor R _ EXT to a first voltage, thereby obtaining a corresponding input current I0[ X ]. In the scheme, a voltage control module is added, namely, the output regulation of the constant current source is divided into two parts, one part is used for regulating the size of the input voltage, and the other part is used for regulating the mirror ratio of the current mirror, so that the value of the input voltage can be designed to be larger, and the influence of the offset voltage of the operational amplifier on the constant current output precision is reduced. When the current gain is set to be smaller, namely the input current is smaller, the processor or the register can synchronously adjust the sizes of the MOS tubes in the current mirror, so that | VGS | (the absolute value of VGS) of the MOS tubes are in a reasonable interval, and the precision of constant current output is improved.
The REXT loop module is used for clamping the voltage across the external resistor R _ EXT to a voltage that is required by a user or a preset voltage, that is, a first voltage referred to in the present invention, and it should be noted that the first voltage referred to in the present embodiment, and a third voltage and a second voltage referred to later are merely distinguished in terms of nomenclature, and do not represent a change in voltage amplitude, and may even be that the third voltage, the first voltage, and the second voltage are identical, that is, the third voltage, the first voltage, and the second voltage are not substantially related in voltage magnitude. Among them, REXT loop module, which is mainly composed of amplifiers, is implemented by using a circuit structure known in the art without being modified by the present invention. For example, in fig. 1, that is, the prior art is configured by using an amplifier AMP1 and an N-type MOS transistor NM0, an input terminal of the amplifier AMP1 is connected to an input voltage, an output terminal thereof is connected to a gate of the N-type MOS transistor NM0, and a source of the N-type MOS transistor NM0 and another input terminal of the amplifier AMP1 are connected to an external resistor R _ EXT. In addition to the implementation shown in fig. 1, the amplifier may be directly formed by an amplifier, that is, the output terminal of the amplifier is directly connected to the external resistor R _ EXT, so that the voltage at one terminal of the external resistor R _ EXT is equal to the output voltage of the amplifier.
Optionally, an input end of the voltage control module is connected to a reference voltage source, the reference voltage source is configured to input a third voltage to the voltage control module, and the reference voltage source is a band gap voltage source, that is, a band gap voltage reference, which is referred to as a band gap for short. The most classical bandgap reference is a temperature independent voltage reference implemented by using the sum of a voltage with positive temperature coefficient and a voltage with negative temperature coefficient, which cancel each other out.
Optionally, the LED display screen constant current source driving module may further include a voltage control module, wherein the input end of the REXT loop module is connected to a reference voltage source, and the reference voltage source is configured to input a third voltage to the REXT loop module.
Optionally, an input channel of the first current mirror is formed by connecting a plurality of P-type MOS transistors, and a switch element is arranged in a connection line of the input channel for controlling the number of connected MOS transistors. When the second current mirrors are connected with the first current mirror in sequence, the output channels of the odd second current mirrors are formed by connecting a plurality of N-type MOS (metal oxide semiconductor) tubes, and the output channels of the even second current mirrors are formed by connecting a plurality of P-type MOS tubes; when the second current mirror is respectively connected with the output channel of the first current mirror, the output channel of the second current mirror is formed by connecting a plurality of N-type MOS tubes, and a connecting circuit of the second current mirror is provided with a switch element for controlling the access quantity of the MOS tubes.
Referring to fig. 6 and 7, in this design, the switching element is implemented by means of a diode, and besides, the switching element may be implemented by a manual knife switch or a relay switch. The switch can be selected according to different application occasions, a diode or a relay switch is selected in a chip or an integrated circuit, and a knife switch mode can be adopted in a large-scale control field open type circuit. That is, in the present invention, there is no specific limitation on the type of the switching element, and any switching element capable of controlling the number of MOS transistors connected may be used in the present invention.
The more the number of the MOS transistors is, the higher the adjustment accuracy is, that is, the wider the adjustment of the width-to-length ratio of the MOS transistor of the channel can be controlled, wherein the circuit diagrams shown in fig. 2 and 3 are equivalent circuits, and do not indicate that the current mirror only includes one MOS transistor, and the oblique arrows on the MOS transistors in fig. 2 and 3 indicate that the width-to-length ratio of the MOS transistor is adjustable. The actual circuit thereof can be seen with reference to fig. 6 and 7.
Optionally, an LED display screen constant current source driving module, the connection mode of the MOS transistors includes parallel connection and series connection, fig. 6 and fig. 7 show the connection mode of the P-type MOS transistor and the N-type MOS transistor respectively, wherein the connection mode of the MOS transistors is series connection or parallel connection, what is shown in fig. 5 and fig. 6 is the parallel connection mode, that is, the width of the MOS transistor assembly is adjusted in the parallel connection mode, because the length of the MOS transistor assembly is fixed, when the width is changed, the width-to-length ratio of the MOS transistor assembly is also changed correspondingly. The series connection is similar, and the difference is that the length of the MOS tube component is adjusted.
Optionally, the current detection module comprises a sampling circuit and a control module, the sampling circuit is connected with the first current mirror, the output current I0 of the first current mirror is sampled, the obtained sampling current is sent to the control module to be compared with the reference current mirror, when the sampling current is larger than the reference current, the mirror proportion of the first current mirror is reduced, if the sampling current is smaller than the reference current, the mirror proportion of the first current mirror is increased until the sampling current is within the reference current threshold interval.
It should be noted that the sampling circuit in the present disclosure refers to a current sampling circuit, and all current sampling circuits known in the art can be used in the present disclosure, and corresponding simple modifications made to the current sampling circuit known in the art without creative work also belong to the protection category of the present disclosure.
Optionally, in the LED display screen constant current source driving module, the sampling circuit preferably samples in a manner of constructing a current mirror to implement sampling, that is, an MOS transistor forming an R _ EXT current mirror with an input channel of the first current mirror is constructed to output a mirror current Icmp [ x ] of an input current I0 of the first current mirror, as described with reference to fig. 10, two R _ EXT current mirrors are respectively constructed by the MOS transistors PM4 and PM5 and the PM0 in the first current mirror, so as to obtain two sampling currents, that is, the mirror currents Icmp [1] and Icmp [2] of the input current I0, except for the example provided in this embodiment, only one MOS transistor and the PM0 may be designed to form an R _ EXT current mirror.
Optionally, in the LED display screen constant current source driving module, an output channel of the R _ EXT current mirror is connected to the control module, and a reference current is set to [ IRB, IRT ], where IRB is a lower limit value of the reference current and IRT is an upper limit value of the reference current; the control module image current Icmp [ X ] is compared with reference current [ IRB, IRT ], when Icmp [ X ] is not in the interval range of the reference current [ IRB, IRT ], the image proportion A [ X ] of the R _ EXT current mirror is adjusted until IRB is smaller than Icmp [ X ] < IRT; the comparison is done separately, i.e., using the resulting mirror currents Icmp [1] and Icmp [2] to compare with reference current IRB and reference current IRT, respectively. If only one R _ EXT current mirror is designed, the internal comparison can be carried out by utilizing the principle of a microprocessor.
Since the first current mirror and the R _ EXT current mirror share the PM0, where the PM0 is a MOS transistor component with adjustable width-to-length ratio, the mirror ratio a [ X ] of the R _ EXT current mirror is adjusted, and at the same time, the mirror ratio K [ X ] of the first current mirror is changed to adjust the output current I1 of the first current mirror, and at the same time, the mirror ratio J [ X ] of the second current mirror is adjusted to make IOUT [ X ] equal to I1 × J [ X ], where I1 is the output circuit of the first current mirror.
Optionally, as shown in fig. 10, the control module includes:
the comparator connected to the output channel of the R _ EXT current mirror is used for inputting the mirror current Icmp [ x ], the reference terminals of the comparator input the reference currents [ IRB, IRT ], in the embodiment, the two comparators input the mirror currents Icmp [1] and Icmp [2] respectively, and the reference input terminals of the two comparators input the reference current IRB and the reference current IRT respectively.
And the logic circuit is connected with the comparator and is used for outputting mirror ratio adjusting instructions of the first current mirror and the second current mirror so as to meet the following requirements:
when Icmp [ X ] is not in the interval range of the reference current [ IRB, IRT ], adjusting the mirror ratio A [ X ] of the R _ EXT current mirror until IRB < Icmp [ X ] < IRT;
meanwhile, the mirror ratio J [ X ] of the second current mirror is adjusted so that IOUT [ X ] is I1 × J [ X ].
Optionally, in the LED display screen constant current source driving module, the adjustment instruction may directly act on the switch element, or a processor or a register is provided, where the processor or the register stores the control instruction of the switch element, and when the adjustment is satisfied, the corresponding control instruction is sent.
Optionally, a LED display screen constant current source drive module, the regulating instruction acts on switching element for control MOS pipe inserts the number, and the regulating instruction includes:
a control signal SP [ M:1] with the width of M bits, which is used for controlling the mirror proportion KX of the first current mirror;
and a control signal SN [ N:1] with N bits of bit width for controlling the mirror ratio JX of the second current mirror;
m is the number of MOS (metal oxide semiconductor) tubes of the input channel of the first current mirror, and N is the number of MOS tubes of the output channel of the second current mirror.
M and N are generally designed to be the same to implement synchronous adjustment of the width-length ratio of the input channel and the output channel, where synchronous adjustment means that the product of the mirror ratio of two corresponding current mirrors remains unchanged during adjustment, which is equivalent to increasing the width of the MOS transistor assembly of the input channel by M times, and increasing the length of the MOS transistor assembly of the output channel by M times, or decreasing the width by M times.
Optionally, in the LED display screen constant current source driving module, the control signal of the adjustment instruction is a binary code, and each bit of the binary code corresponds to a control signal of an MOS transistor;
wherein 0 represents on and 1 represents off;
or, 1 indicates on and 0 indicates off.
A constant current source driving control method of an LED display screen uses the LED display screen constant current source driving module, and the method comprises the following steps:
step S1: dividing the output current of the constant current source module into L sections;
step S2: the present constant current source module works in the section X current, the output current is IOUT [ X ], the mirror ratio of the first current mirror is KX, the mirror ratio of the second current mirror is J [ X ], the input current of the first current mirror is I0[ X ], then: IOUT [ X ] ═ I0[ X ] × J [ X ] × K [ X ];
step S3: when the constant current source module works at the (X + 1) th section of current, the voltage at the two ends of the external resistor R _ EXT is clamped to the first voltage through the REXT loop module, the input current of the first current mirror is I0 (X + 1), and the method comprises the following steps:
the output current is IOUT [ X +1] ═ I0[ X +1] × K [ X +1] × J [ X +1], and K [ X +1] ═ J [ X ] × K [ X ].
Furthermore, the output current of the constant current source module is increased from the 1 st section to the L th section in sequence, then K [ X +1] < K [ X ], J [ X +1] > J [ X ], that is, when the output current is changed from IOUT [ X ] to IOUT [ X +1], the mirror ratio of the first current mirror is reduced, and the mirror ratio of the second current mirror is increased;
or;
when the output current of the constant current source module is reduced from the 1 st section to the L th section in sequence, K [ X +1] > K [ X ], J [ X +1] < J [ X ], that is, when the output current is changed from IOUT [ X ] to IOUT [ X +1], the mirror ratio of the first current mirror is increased, and the mirror ratio of the second current mirror is reduced.
Further, the method also comprises an output current section selection control method of the constant current source module, which comprises the following steps:
step S01: obtaining a mirror current Icmp [ x ] of the R _ EXT current mirror;
step S02: comparing the mirror current Icmp [ X ] with the reference current [ IRB, IRT ], and when the Icmp [ X ] is not in the interval range of the reference current [ IRB, IRT ], adjusting the mirror proportion A [ X ] of the R _ EXT current mirror until IRB is smaller than Icmp [ X ] < IRT;
wherein, IRB is the lower limit value of the reference current, and IRT is the upper limit value of the reference current.
Further, the specific step of step S02 is:
when the IRB < Icmp [ X ] < IRT is detected, the chip works in a state of a mirror image proportion A [ X ] of a current segment X and a mirror image proportion of an R _ EXT current mirror, namely the mirror image proportion of a first current mirror is KX;
when Icmp [ X ] < IRB is detected, the current segment of the chip work is changed from the Xth segment to the X-1 th segment, the mirror image proportion of the R _ EXT current mirror is changed from A [ X ] to A [ X-1], wherein A [ X-1] < A [ X ], the mirror image proportion of the first current mirror is changed from K [ X ] to K [ X-1], the mirror image current Icmp [ X ] is increased, and the next round of detection is carried out until IRB < Icmp [ X ] < IRT is detected;
when Icmp [ X ] IRT is detected, the current segment of the chip work is changed from the Xth segment to the X +1 th segment, the mirror ratio of the R _ EXT current mirror is changed from A [ X ] to A [ X +1], wherein A [ X ] is larger than A [ X +1], the mirror ratio of the first current mirror is changed from K [ X ] to K [ X +1], the mirror current Icmp [ X ] is reduced, and the next round of detection is carried out until IRB < Icmp < IRT is detected.
Normally, I1 can only fluctuate within a certain range in a fixed circuit, because the mirror ratio K of the first current mirror is determined by the number of MOS transistors in the MOS transistor assembly, and it can be satisfied that the value of K is continuous only when the number of MOS transistors approaches infinity, and the value of K is usually a fixed value, for example, 10 MOS transistors are in a MOS transistor assembly, and the value of K is 10 (assumed to be 1-10), and it can be ensured that I1 is fixed only when the output current IOUT just works at the 10 points.
For example, the output current IOUT is 10A, the input current I0 is 1A, K is 1, J is 10, and then IOUT is 10A is 1A 1 x 10;
at this time, the output current IOUT becomes 20A, and if J × K is constant, I0 is 2A, and if I1 is 1A, K is 2/1 is 2, and J correspondence becomes 5, I1 is maintained as 1A. In practice, this will not generally occur, I1 will remain unchanged only when such coincidence occurs.
At this time, when the output current IOUT becomes 9A, I0 is 0.9A, and if it is required to satisfy J × K, I1 is 1A, K is 1/0.9, and it is obvious that K does not include this value in practice, and therefore, only one value K close to this value, that is, K is 1, and I1 is 0.9A. That is, in practical situations, it is generally impossible to maintain I1 unchanged, and this state can only be realized under ideal conditions.
Referring to fig. 9, a specific example of the present invention is shown, and the control method includes:
1) when the drain potential of PM2 is clamped to VREF1 by the operational amplifier AMP1, the current flowing through PM0 and R _ EXT is I0 — VREF1/R _ EXT;
2) the PM1 and the PM0 form a current mirror, mirror the current I0 flowing through the R _ EXT resistor to generate a current I1, and output the current I1 to the NM 1.
3) NM1 and NM _ C0 form a current mirror, which mirrors the current I1 to generate the output current IOUT of the channel;
4) in the current detection module, PM4, PM5 and PM0 form an R _ EXT current mirror, mirror currents Icmp1 and Icmp2 (Icmp 1 is designed as Icmp2 is designed as Icmp) of I0 are generated and compared with IRT and IRB respectively, and according to the detection result, a logic circuit generates corresponding segment selection control signals SP [ L:1] and SN [ L:1], and the segment selection control signals SP [ L:1] and SN [ L:1] are used for controlling the number of on-state MOS transistors in PM0[ L:1] and NM _ C0[ L:1] respectively. When SN [ X ] and SP [ X ] are effective, VGNO [ X ] is VGN and VGPO [ X ] is VGP; when S [ X ] is invalid, VGNO [ X ] is GND and VGPO [ X ] is VDD.
5) When IRB < Icmp < IRT is detected, the chip works in a correct current segment, segment selection control signals SP [ L:1] and SN [ L:1] are kept unchanged, the number of the opened MOS tubes in PM0[ L:1] and NM _ C0[ L:1] is kept unchanged, the mirror ratio a X K [ X ] of Icmp and I0 is kept unchanged, and the mirror current Icmp is kept unchanged.
6) When detecting Icmp < IRB, the segment selection control signals SP [ L:1] and SN [ L:1] are changed, the current segment of the chip operation is changed from the X-th segment to the X-1-th segment, the number of the MOS tubes in PM0[ L:1] and NM _ C0[ L:1] which are opened is reduced, the mirror ratio of Icmp and I0 is changed from a K [ X ] to a K [ X +1], wherein a K [ X ] is A [ X ], the mirror current Icmp is increased, and the next round of detection is carried out until detecting the IRB < Icmp < IRT.
7) When the Icmp > IRT is detected, the segment selection control signals SP [ L:1] and SN [ L:1] are changed, the current segment of the chip operation is changed from the X-th segment to the X + 1-th segment, the number of the MOS tubes in PM0[ L:1] and NM _ C0[ L:1] which are started is increased, the mirror ratio of the Icmp and I0 is changed from A [ X ] to A [ X-1], the mirror current Icmp is reduced, and the next round of detection is carried out until the IRB < Icmp < IRT is detected.
In the method, under the condition of meeting the constant current output precision, the current I1 can be designed to be small enough and not to change greatly along with the change of the output constant current, so that the | VGS | (the absolute value of VGS) of PM0, PM1 and NM1 and each channel NM _ C0 are all in a larger value, the power consumption of the constant current driving chip can be effectively reduced, and the precision of constant current output can be improved.
The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (18)
1. The utility model provides a LED display screen constant current source drive module which characterized in that includes:
the REXT loop module is connected with the external resistor R _ EXT and used for clamping the voltage at two ends of the external resistor R _ EXT to a first voltage;
the REXT loop module comprises a first current mirror connected with the REXT loop module and one or more second current mirrors connected with the first current mirror, wherein an input channel of the first current mirror and an output channel of the second current mirror are formed by connecting a plurality of MOS (metal oxide semiconductor) tubes, so that the mirror ratio of the first current mirror and the second current mirror is adjustable;
the current detection module is connected with the first current mirror and is used for detecting the output current of the first current mirror and outputting mirror image proportion control instructions of the first current mirror and the second current mirror;
the first current mirror and the second current mirror perform mirror proportion adjustment according to the control instruction, so that the output current I1 of the first current mirror fluctuates within a fixed range.
2. The LED display screen constant current source driving module according to claim 1, wherein the second current mirror is connected to the first current mirror in sequence, or the second current mirror is connected to the output channel of the first current mirror respectively.
3. The constant current source module of claim 2, wherein the REXT loop module input is connected to a voltage control module, the voltage control module being configured to regulate the input voltage of the REXT loop module to a second voltage.
4. The LED display screen constant current source driving module as claimed in claim 3, wherein the input terminal of the voltage control module is connected to a reference voltage source, and the reference voltage source is used for inputting a third voltage to the voltage control module.
5. The LED display screen constant current source driving module as claimed in claim 4, wherein the REXT loop module input terminal is connected to a reference voltage source, and the reference voltage source is used for inputting a third voltage to the REXT loop module.
6. The LED display screen constant current source driving module according to any one of claims 1-5, wherein the input channel of the first current mirror is formed by connecting a plurality of P-type MOS transistors, and a switching element is disposed in the connecting circuit for controlling the number of the MOS transistors.
7. The LED display screen constant current source driving module according to claim 6, wherein when the second current mirrors are sequentially connected to the first current mirror, the output channels of the odd second current mirrors are formed by connecting a plurality of N-type MOS transistors, and the output channels of the even second current mirrors are formed by connecting a plurality of P-type MOS transistors;
when the second current mirror is respectively connected with the output channel of the first current mirror, the output channel of the second current mirror is formed by connecting a plurality of N-type MOS tubes, and a connecting circuit of the second current mirror is provided with a switch element for controlling the access quantity of the MOS tubes.
8. The LED display screen constant current source driving module according to claim 7, wherein the MOS transistors are connected in parallel and in series.
9. The LED display screen constant current source driving module according to any one of claims 1-8, wherein the current detection module comprises a sampling circuit and a control module, the sampling circuit is connected to the first current mirror, samples the output current I0 of the first current mirror, sends the obtained sampling current to the control module to compare with the reference current mirror, and when the sampling current is greater than the reference current, reduces the mirror ratio of the first current mirror, and if the sampling current is less than the reference current, increases the mirror ratio of the first current mirror until the sampling current is within the reference current threshold interval.
10. The LED display screen constant current source driving module as claimed in claim 9, wherein the sampling circuit is a MOS transistor forming an R _ EXT current mirror with the input channel of the first current mirror, and configured to output the mirror current Icmp [ x ] of the first current mirror input current I0.
11. The LED display screen constant current source driving module according to claim 10, wherein the R _ EXT current mirror output channel is connected to the control module, and the reference current is set as [ IRB, IRT ], where IRB is a lower limit value of the reference current and IRT is an upper limit value of the reference current;
the control module image current Icmp [ X ] is compared with reference current [ IRB, IRT ], and when Icmp [ X ] is not in the interval range of the reference current [ IRB, IRT ], the image proportion A [ X ] of the R _ EXT current mirror is adjusted until IRB is smaller than Icmp [ X ] < IRT;
meanwhile, the mirror ratio J [ X ] of the second current mirror is adjusted so that IOUT [ X ] is I1 × J [ X ], where I1 is the output circuit of the first current mirror.
12. The LED display screen constant current source driving module as claimed in claim 11, wherein the control module comprises:
the comparator is connected with an output channel of the R _ EXT current mirror and used for inputting a mirror current Icmp [ x ], and a reference end of the comparator inputs a reference current [ IRB, IRT ];
and the logic circuit is connected with the comparator and is used for outputting mirror ratio adjusting instructions of the first current mirror and the second current mirror so as to meet the following requirements:
when Icmp [ X ] is not in the interval range of the reference current [ IRB, IRT ], adjusting the mirror ratio A [ X ] of the R _ EXT current mirror until IRB < Icmp [ X ] < IRT;
meanwhile, the mirror ratio J [ X ] of the second current mirror is adjusted so that IOUT [ X ] is I1 × J [ X ].
13. The LED display screen constant current source driving module according to claim 12, wherein the adjusting instructions act on the switching elements for controlling the number of MOS transistors connected, and the adjusting instructions include:
a control signal SP [ M:1] with the width of M bits, which is used for controlling the mirror proportion KX of the first current mirror;
and a control signal SN [ N:1] with N bits of bit width for controlling the mirror ratio JX of the second current mirror;
m is the number of MOS (metal oxide semiconductor) tubes of the input channel of the first current mirror, and N is the number of MOS tubes of the output channel of the second current mirror.
14. The LED display screen constant current source driving module according to claim 13, wherein the control signal of the adjustment command is binary coded, and each binary number in the binary coded corresponds to a control signal of an MOS transistor;
wherein 0 represents on and 1 represents off;
or, 1 indicates on and 0 indicates off.
15. An LED display screen constant current source driving control method, using an LED display screen constant current source driving module according to any one of claims 1 to 14, the method comprising:
step S1: dividing the output current of the constant current source module into L sections;
step S2: the current constant current source module works in the Xth section current, the output current is IOUT [ X ], the mirror ratio of the first current mirror is KX, the mirror ratio of the second current mirror is JX, the input current of the first current mirror is I0[ X ],
then there are: IOUT [ X ] ═ I0[ X ] × J [ X ] × K [ X ];
step S3: when the constant current source module works at the (X + 1) th section of current, the voltage at the two ends of the external resistor R _ EXT is clamped to the first voltage through the REXT loop module, the input current of the first current mirror is I0 (X + 1), and the method comprises the following steps:
the output current is IOUT [ X +1] ═ I0[ X +1] × K [ X +1] × J [ X +1], and K [ X +1] ═ J [ X ] × K [ X ].
16. The method according to claim 15, wherein when the output current of the constant current source module increases from the 1 st segment to the L th segment, K [ X +1] < kx, jx +1] > jx, that is, when the output current changes from IOUT [ X ] to IOUT [ X +1], the mirror ratio of the first current mirror decreases and the mirror ratio of the second current mirror increases;
or;
when the output current of the constant current source module is reduced from the 1 st section to the L th section in sequence, K [ X +1] > K [ X ], J [ X +1] < J [ X ], that is, when the output current is changed from IOUT [ X ] to IOUT [ X +1], the mirror ratio of the first current mirror is increased, and the mirror ratio of the second current mirror is reduced.
17. The LED display screen constant current source driving control method of claim 16, further comprising an output current segment selection control method of the constant current source module, comprising:
step S01: obtaining a mirror current Icmp [ x ] of the R _ EXT current mirror;
step S02: comparing the mirror current Icmp [ X ] with the reference current [ IRB, IRT ], and when the Icmp [ X ] is not in the interval range of the reference current [ IRB, IRT ], adjusting the mirror proportion A [ X ] of the R _ EXT current mirror until IRB is smaller than Icmp [ X ] < IRT;
wherein, IRB is the lower limit value of the reference current, and IRT is the upper limit value of the reference current.
18. The method for controlling the driving of the LED display screen constant current source according to claim 17, wherein the step S02 comprises the following steps:
when the IRB < Icmp [ X ] < IRT is detected, the chip works in a state of a mirror image proportion A [ X ] of a current segment X and a mirror image proportion of an R _ EXT current mirror, namely the mirror image proportion of a first current mirror is KX;
when Icmp [ X ] < IRB is detected, the current segment of the chip work is changed from the Xth segment to the X-1 th segment, the mirror image proportion of the R _ EXT current mirror is changed from A [ X ] to A [ X-1], wherein A [ X-1] < A [ X ], the mirror image proportion of the first current mirror is changed from K [ X ] to K [ X-1], the mirror image current Icmp [ X ] is increased, and the next round of detection is carried out until IRB < Icmp [ X ] < IRT is detected;
when Icmp [ X ] IRT is detected, the current segment of the chip work is changed from the Xth segment to the X +1 th segment, the mirror ratio of the R _ EXT current mirror is changed from A [ X ] to A [ X +1], wherein A [ X ] is larger than A [ X +1], the mirror ratio of the first current mirror is changed from K [ X ] to K [ X +1], the mirror current Icmp [ X ] is reduced, and the next round of detection is carried out until IRB < Icmp < IRT is detected.
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| TWI807725B (en) * | 2022-03-25 | 2023-07-01 | 大陸商北京集創北方科技股份有限公司 | Trimming circuit, LED display driver chip and LED display device |
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Also Published As
| Publication number | Publication date |
|---|---|
| CN113851078A (en) | 2021-12-28 |
| CN113851076A (en) | 2021-12-28 |
| CN113851078B (en) | 2023-07-11 |
| CN113851077A (en) | 2021-12-28 |
| CN214752879U (en) | 2021-11-16 |
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