Micro-LED is a current-driven light-emitting gadget, and its driving mode typically has solely two modes: passive addressing drive (PM: Passive Matrix, also called passive addressing, passive addressing, passive drive, and so on.) and energetic Addressing drive (AM: Lively Matrix, also called energetic addressing, energetic addressing, energetic drive, and so on.), this text may also analyze a “semi-active” addressing drive technique. These modes have totally different driving ideas and utility traits, and the next will introduce their ideas intimately by way of the circuit diagram.
What’s PM drive mode?
Passive addressing drive mode connects the anode (P-electrode) of every column of LED pixels within the array to the column scan line (Information Present Supply), and on the similar time connects the cathode (N-electrode) of every row of LED pixels to the row scan Line (Scan Line).
When a selected scan line in column Y and row X is chosen, the LED pixel on the intersection level (X, Y) might be lit. On this manner, all the display screen could be scanned level by level at excessive velocity to comprehend the show image, as proven in Determine 1. This scanning technique has a easy construction and is comparatively simple to implement.
However the drawback is that the connection is difficult (X+Y connection is required), the effectivity is low as a result of massive parasitic resistance and capacitance, the pixel light-emitting time is brief (1 discipline/XY), which ends up in low efficient brightness, simple crosstalk between pixels, and The frequency requirement of the scanning sign is excessive.
One other optimized passive handle choice driving technique is so as to add a latch within the column scanning half, and its operate is to retailer the column scanning indicators (Y1, Y2… Yn) of all pixels in row X at a sure second within the latch prematurely. gadget.
When row X is chosen, the above-mentioned Y1-Yn indicators are loaded on the pixels on the similar time. This driving technique can scale back the frequency of the column driving sign and enhance the brightness and high quality of the displayed image. Nevertheless, it’s nonetheless unable to beat the inherent defects of the passive handle choice drive technique: the connection is complicated, simple to crosstalk, and the pixel strobe sign can’t be preserved. The energetic handle choice drive technique gives a very good answer for the above difficulties.
What’s AM drive mode?
Within the energetic address-selection driving circuit, every Micro-LED pixel has its corresponding unbiased driving circuit, and the driving present is supplied by the driving transistor. The essential energetic matrix drive circuit is a two-transistor single-capacitor (2T1C: 2 Transistor 1 Capacitor) circuit, as proven in Determine 2.
Determine 2 Lively addressing drive mode
At the least two transistors are utilized in every pixel circuit to manage the output present, and T1 is a gate transistor, which is used to manage the on or off of the pixel circuit. T2 is to drive a transistor, which is related with a voltage supply and gives a steady present for the Micro-LED inside a body.
There’s additionally a storage capacitor C1 within the circuit to retailer the information sign (Vdata). When the scanning sign pulse of the pixel unit ends, the storage capacitor can nonetheless keep the voltage of the gate of the driving transistor T2, in order to drive the Micro-LED pixel constantly till the tip of the Body.
The 2T1C drive circuit is simply a primary pixel circuit construction for energetic addressing Micro-LEDs, and its construction is comparatively easy and straightforward to implement. Nevertheless, since its essence is a voltage-controlled present supply (VCCS), and the Micro-LED pixel is a current-type gadget, it can carry sure difficulties within the management of the show grayscale. Mentioned within the Transformation and Grayscale part.
Dr. Liu Zhaojun’s analysis group as soon as proposed a 4T2C present proportional Micro-LED pixel circuit, which makes use of a current-controlled present supply (CCCS) technique, which has benefits in realizing grey scale.
What’s the “semi-active” addressing drive technique?
One other factor that must be talked about is a “semi-active” addressing drive technique. This driving technique makes use of a single transistor because the driving circuit of the Micro-LED pixel (as proven in Determine 3), in order that crosstalk between pixels could be higher averted.
Comparability of three driving strategies
In contrast with passive addressing, energetic addressing has apparent benefits and is extra appropriate for current-driven light-emitting units comparable to Micro-LEDs. The detailed evaluation is as follows:
① The driving means of energetic web site choice is stronger, which might understand the driving of bigger space. Nevertheless, the driving functionality of passive handle choice is affected by the driving efficiency of the exterior built-in circuit, and the driving space and determination are restricted
② Lively web site choice has higher brightness uniformity and distinction. Within the passive addressing mode, as a result of restricted driving functionality of the exterior driving built-in circuit, the brightness of every pixel is affected by the variety of lit pixels on this column. Usually talking, the Micro-LED pixels in the identical column share the drive present of a number of output pins of the exterior drive I
Due to this fact, when the variety of lighted pixels within the two columns is totally different, the driving present utilized to every LED pixel might be totally different, and the brightness of various columns will differ vastly. This drawback might be extra significantly mirrored in large-area show functions, comparable to led screen solutions TVs and LED massive screens. On the similar time, because the variety of rows and columns will increase, this drawback will turn out to be extra sever
③ Lively web site choice can obtain low energy consumption and excessive effectivity. Giant-area show functions require a comparatively massive pixel density, so the electrode measurement have to be diminished as a lot as doable, and the voltage required to drive the show may also enhance vastly, and a considerable amount of energy might be misplaced on the row and column scan traces. leading to inefficienci
.
④ Excessive unbiased controllability. In passive handle choice, greater drive voltage may also carry the second bother, that’s, crosstalk, that’s to say, in passive handle LED array, the drive present theoretically solely passes by way of the chosen LED pixels, however Different surrounding pixels might be affected by the present pulse, which can finally degrade the show high quality. The energetic handle choice technique avoids this phenomenon very nicely by way of the pixel circuit composed of a cross transistor and a drive transis
r.
⑤ Larger decision. Lively handle choice drives are extra appropriate for Micro-LED shows with excessive PPI and excessive resolu
on.
Though the third “semi-active” drive can higher keep away from the crosstalk phenomenon between pixels, however as a result of there is no such thing as a storage capacitor within the pixel circuit, and the driving present sign of every column must be modulated individually, it can’t totally obtain the above column. All the benefits of the energetic addressing drive me
od.
Taking the blue-light Micro-LED epitaxially grown on a sapphire substrate for instance, there are 4 methods to attach the pixel and the driving transistor T2 as proven in FIG. 4 . Nevertheless, for the reason that LED epitaxial progress construction is p-type gallium nitride (GaN) on the outermost floor and n-type gallium nitride on the underside layer, as proven in Figu
From the attitude of producing course of, it’s extra cheap to attach the output terminal of the driving transistor to the p-electrode of the Micro-LED pixel, particularly (a) and (c) in Determine 4. In Determine 4(a), the Micro-LED pixel is related to the supply (Supply) of the N-type drive transistor. The inhomogeneity of Micro-LED electrical traits attributable to the inhomogeneity of epitaxial progress (Epitaxial Progress), manufacturing course of, and gadget getting older will instantly have an effect on the VGS of the driving transistor, leading to uneven show im
es.
The Micro-LED pixel in Determine 4(c) is related to the drain of the P-type drive transistor (Drain), which might keep away from the above-mentioned results, and its current-voltage relationship is proven in Determine 6. Due to this fact, it’s extra applicable to have a P-tube pixel circuit to drive Micro-LED.
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