CN102622958B - Local matching-based multichannel LED constant current source driving circuit - Google Patents

Abstract

The invention, which belongs to the microelectronic and LED drive technology field, provides a local matching-based multichannel LED constant current source driving circuit structure with low mismatching. The circuit comprises a VG generator, a current source ID, a current source mirror, n channels and k Mref subcircuits. More specifically, the VG generator generates grid voltages provided for a power tube and a Mref in the circuit according to the circuit demand; the n channels share a VG in common; the current source ID reproduces current sources for different channel in the system; the current source mirror reproduces the ID and generates k different equal current sources that respectively flow through the k Mref subcircuits. According to the provided circuit structure, a local matching measure can be taken, thereby substantially reducing the total reproduction mismatching.

Description

A kind of multi-channel LED constant current source driving circuit based on local matching

Technical field

The present invention relates to a kind of low mismatch multi-channel LED constant current source driving circuit structure based on local matching, belong to microelectronics and LED Driving technique field.

Background technology

The use of LED screen is at present very extensive, and all there are very large demand in the industry-by-industries such as telecommunications, postal service, finance, traffic and stadiums and government work department to LED screen.Because LED is the device of characteristic sensitivity, and along with temperature variation is remarkable, be greater than after on state threshold voltage at LED lamp, on it, electric current is with the variation acute variation of voltage, and electric current on brightness and LED is directly proportional, therefore need LED to drive to ensure reliability and the display consistency of LED.Linearity when consistance when interchannel currents match can ensure different pixels point demonstration same grayscale and different gray scale.The LED drive circuit of low mismatch can be used in the LED screen of high display quality.

Fig. 1 has provided a kind of structural drawing of typical traditional LED drive circuit.This structure comprise a voltage generating module VGEN and n passage (Channel 1, Channel 2 ..., Channel is n).VGEN module provides reference voltage for passage, and its structure comprises an amplifier Opa1, a current mirror (Current Source Mirror), and VG produces circuit (VGGenerator) and two feedback metal-oxide-semiconductor M0 and Mref.This structure need to be inputted 1, one outer meeting resistance Rext of a reference voltage Vref.Because Opa1 enlargement factor is very large, make the drain terminal voltage of M0 equal Vref1 by feedback, calculate ID=Vref1/Rext.ID copies to Iref electric current by current mirror, and VG generation circuit offers the biasing of power tube in Mref and each passage according to VG voltage of circuit requirements generation.Each passage comprises an amplifier and two power tubes (being M1 and Mo1 for passage 1), and because the current ratio of LED is larger, the current ratio flowing through on M1 and Mo1 is larger, needs M1 and the Mo1 of larger area.Between n passage, be duplicate on circuit structure, the coupling that different passages copy Mref has determined different interchannel consistance.Due to power tube, M1 is generally operational in linear zone, and its current replication mismatch may be calculated:

$\frac{\mathrm{\ΔIout}}{\mathrm{Iout}}=\frac{\mathrm{\Δ}\left(\frac{W}{L}\right)}{\left(\frac{W}{L}\right)}+\frac{\mathrm{\Δ}\left(V_{\mathrm{TH}}\right)}{(V_{\mathrm{GS}}-V_{\mathrm{TH}})}+\frac{\mathrm{\Δ}\left({\mathrm{\μC}}_{\mathrm{ox}}\right)}{\left({\mathrm{\μC}}_{\mathrm{ox}}\right)}+\frac{\mathrm{\Δ}\left(V_{\mathrm{ref}2}\right)}{\left(V_{\mathrm{ref}2}\right)}$

The structure that Fig. 1 provides is in the time of current replication, and the mismatch that process deviation causes is very large.The different interchannel mismatches of this structure are mainly from breadth length ratio mismatch, threshold voltage mismatch, μ C _oxmismatch and Vref2 copy mismatch.Wherein breadth length ratio mismatch, threshold voltage mismatch and μ C _oxmismatch belongs to the error of introducing in technological process, and the mismatch that copies of Vref2 is caused by the offset voltage of amplifier.If adopt the amplifier of low maladjustment voltage, current replication mismatch is greatly from fabrication error.Fig. 2 has provided the domain of the circuit structure (taking 8 channel LED driving circuits is example) of Fig. 1 and has realized schematic diagram.Can find because the area of power tube is very large, for multichannel LED drive circuit, different passages are positioned at the diverse location of domain, not only far apart from the position of Mref, and different interchannel distances are also far, its different interchannel power tubes cannot or be difficult to mate to reduce mismatch by do for example common centroid of local matching on domain.Therefore process deviation is to cause the unmatched main cause of different interchannels.

Summary of the invention

The present invention proposes a kind of low mismatch multi-channel LED constant current source driving circuit structure based on local matching, make the circuit structure after improving can on domain, carry out coupling.

The structure that the present invention proposes comprises a VG and produces circuit (VG Generator), a current source ID, a current mirror (Current Source Mirror), n passage, k bar Mref branch road (1 < k≤n, k=1 is Fig. 1 structure).It is to produce the grid voltage to power tube in circuit and Mref according to circuit requirements that described VG produces circuit, can be a constant voltage, can be also other organization plans such as the different voltages that change with different I D.In described circuit structure, identical VG of n channels share.Described current source ID is the electric current source that in system, different passages copy, and can be outside input, can be also other sources such as inside circuit generation.Described current mirror (Current Source Mirror) copies ID and produces k different identical currents source, called after Iref1 respectively, and Iref2, Iref3 ..., Irefk.Described current mirror can be simple cascade, can be also other structures.A described k current source flows through respectively k Mref branch road.

In described k bar Mref branch road, every branch road comprises a metal-oxide-semiconductor, and the grid of metal-oxide-semiconductor meets VG and produces the VG voltage that circuit produces, on it, flow through corresponding electric current I refi (i=1,2,3, ..., k), this metal-oxide-semiconductor is defined as Mrefi (i=1,2,3 ..., k), on it, drain terminal voltage is defined as VDi (i=1,2,3 ..., k).

In a described n passage, between different passages, structure is consistent, and each passage comprises an amplifier and two power tubes (being for example M1-1 and Mo1-1), a termination VDi of amplifier, the drain terminal (first passage) of another termination M1-1.Because the enlargement factor of amplifier is very large, the drain terminal voltage of M1-1 is approximately equal to VDi, has realized copying of VDi.In a described n passage, Mref branch road of every n/k channels share, the VDi that this n/k channels share is identical.Define i passage corresponding to Mref branch road and be respectively Mrefi-1, Mrefi-2 ..., Mrefi-(n/k).

In the domain structure of described circuit structure.(Current Source Mirror) is adjacent on domain position for current mirror module, and takes coupling measure; The power tube of i article of Mref branch road Mrefi and its corresponding n/k passage is adjacent on domain position, and takes coupling measure, and i is all like this from 1 to k.In described domain structure, Mrefi is in the center of the power tube of n/k passage.

Multiple current sources that in the structure that the present invention proposes, different passage replica current mirrors produce, every n adjacency channel is shared a current source (can take different n values for different application, the higher n value of matching degree requirement just need to be less).On domain, all can adopt for example way of common centroid coupling of local matching, in traditional structure, the shared road current source of employing, can well be mated.In the structure that the present invention proposes, copy the measure that all can adopt local matching, greatly reduce so totally copy mismatch.With respect to traditional structure, the whole process of different interchannel current replication prime electric currents all can be done local matching treatment, and the domain of circuit structure is insensitive to process deviation, thereby can improve the different interchannel couplings that copy.

Brief description of the drawings

Fig. 1 is the LED drive circuit of traditional structure;

Fig. 2 is the domain structure schematic diagram that traditional circuit adopts;

Fig. 3 is the LED drive circuit that the present invention proposes;

Fig. 4 is the domain that the circuit structure that proposes of the present invention adopts.

Embodiment

Below in conjunction with accompanying drawing, by specific embodiment, technical scheme of the present invention is described in further detail.

Fig. 3 is the physical circuit figure of the structure embodiment that proposes of the present invention, as shown in Figure 3, has provided 4 passages (n=4) in figure, channel1-1, channel1-2, channel2-1, channel2-2, the schematic diagram of every 2 channels share, one road Mref branch road (k=4/2=2), channel1-1, channel1-2 shares Mref1 branch road, use amplifier to copy VD1, channel2-1, channel2-2 shares Mref2 branch road, uses amplifier to copy VD2.Current Source Mirror in structural drawing is first order current mirror, copies prime current source ID and produces 2 by current source Iref1 and the Iref2 of Mref, and this reproduction process produces a mismatch; Second mismatch is the copy mismatches of different passages to corresponding Mref, wherein channel1-1, and channel1-2 copies Iref1, channel2-1, channel2-2 copies Iref2.As long as when the each generation of guarantee current replication, two corresponding metal-oxide-semiconductors mate, just can ensure to copy the accurate of multiple, thereby whole reproduction process is all accurate.First Iref1 and Iref2 mate, and Mref1 and Mref2 do not mate be exist but do not affect coupling because be also not mating of equal numbers value between Mref and corresponding different interchannels.

Fig. 4 is the concrete domain of the structure embodiment that proposes of the present invention, as shown in Figure 4, has provided in 8 channel LED driving circuits the domain schematic diagram of a Mref branch road of every 4 channels share in figure.Get n=8, k=2, Mref branch road of n/k=4 channels share.Just have four adjacency channel 1-4 to copy Mref1 and belong to local matching, four adjacency channel 5-8 copy Mref2 and also belong to local matching.The electric current flowing through on Mref1 and Mref2 belongs to local matching in the first order copies.The mismatch that copies introducing for twice all belongs to local mismatches, greatly reduces and copies mismatch.

The circuit structure that the present invention proposes has utilized the characteristic of technological process, takes local matching.Mismatch term while analyzing current replication.First,, due in actual process, passing threshold injects adjusting threshold voltage to required value conventionally.The doping content that the voltage swing of threshold voltage and threshold value are injected is closely bound up, and for the metal-oxide-semiconductor that is in domain diverse location, doping content exists gradient, the doping content difference of difference.Secondly, gate oxide thickness is very thin, and representative value is 1/10 of technique L minimum value conventionally.Gate oxide thickness is controlled by oxidization time etc., and its absolute value exists error.For the metal-oxide-semiconductor of complicated technology, there is larger deviation in the gate oxide thickness of diverse location metal-oxide-semiconductor.For example doping content, impurity concentration of the carrier mobility in MOSFET when work and raceway groove environment is relevant, and more close process environments mobility is more close; Threshold voltage and channel doping and gate oxide thickness etc. are relevant, and more close process environments threshold voltage differs less; Breadth length ratio and Cox item are also like this.In order well to be mated, the metal-oxide-semiconductor that needs coupling need to be from better close to must be more in domain process, or realize coupling with common centroid complementation.Moreover, local matching has also reduced in current replication process, and the dead resistance electric capacity of introducing when different interchannels copy does not mate the mismatch of introducing.

The structure that the present invention proposes has realized the different interchannel couplings of LED drive circuit, utilizes the characteristic of domain to realize the local matching in reproduction process.

Claims (4)

1. a LED constant current source driving circuit, it is characterized in that, comprise that a VG produces circuit, a current source ID, a current mirror, n passage and k bar Mref branch road, wherein 1<k≤n, described VG produces circuit and produces the grid voltage VG to power tube in circuit and Mref according to circuit requirements, identical VG of n channels share, described current source ID is the electric current source that in system, different passages copy, described current mirror copies ID and produces k different identical currents source, a described k current source flows through respectively k Mref branch road, in described k bar Mref branch road, every branch road comprises a metal-oxide-semiconductor, the grid of metal-oxide-semiconductor meets VG and produces the VG voltage that circuit produces, on it, flow through corresponding electric current I refi (i=1, 2, 3, k), this metal-oxide-semiconductor is defined as Mrefi (i=1, 2, 3, k), on it, drain terminal voltage is defined as VDi (i=1, 2, 3, k).

2. LED constant current source driving circuit as claimed in claim 1, is characterized in that, it is a constant voltage that described VG produces circuit, can be also other organization plans such as the different voltages that change with different I D.

3. LED constant current source driving circuit as claimed in claim 1, it is characterized in that, in a described n passage, Mref branch road of every n/k channels share, the VDi that this n/k channels share is identical, defines i passage corresponding to Mref branch road and is respectively Mrefi-1, Mrefi-2,, Mrefi-(n/k).

4. LED constant current source driving circuit as claimed in claim 1, is characterized in that, described current mirror module is adjacent on domain position, and takes coupling measure; The power tube of i article of Mref branch road Mrefi and its corresponding n/k passage is adjacent on domain position, and takes coupling measure, and i is all like this from 1 to k.