Overall speed increase - higher refresh rate and frame change frequency
The LED is driven by the current flowing through, and the pulse width can control the brightness and gray level of the LED. Simply speaking, regardless of the design of the system side, the refresh rate is based on the addressing time (Tacc) and the flow. The current rate of the LED is determined by the current speed; the increase of the frame rate requires faster addressing time in addition to the support of the system, and the addressing time and the transmission clock (DCLK) and the number of addressing are Strong positive correlation.
For example, if there is a full-color outdoor display with a number of addressing of 768, the overall addressing time will be different if different clocks are used.
Working clock is 10Mhz - 768X0.1us = 76.8us
Working clock is 30Mhz- 768X0.033us = 25.6us
The speed at which the current flows through the LED determines the refresh rate of the LED display. For example, if an LED display has an address number of 768, a working clock of 30 Mhz, a grayscale adjustment of 8 bits (bits), and brightness adjustment. It is 2 bits (bits), the interval time between each subfield is 4us; the traditional driver chip shows a pulse width of 250ns, and the pulse width of the SnapDrive driver chip is 50ns, the refresh rate of the two can be significantly different.
A. Traditional driver chip (pulse width is 250ns)
The weights are arranged as 1/64, 1/32, 1/16, 1/8, 1/4, 1/2, 1, 2, 4, 8, 16, 32
Tfr=25.6usx[6+63]+5x4us = 1786.4us
Fr = 559.7Hz
B.SnapDrive driver chip (pulse width is 50ns)
The weights are 1/512, 1/256, 1/128, 1/64, 1/32, 1/16, 1/8, 1/4, 1/2, 1, 2, 4
Tfr=25.6usx[9+7]+8x4us=441.6us
Fr=2264.5Hz
Show grayscale improvement
The OE response time of the conventional general-purpose driver chip currently on the market is about 250 ns. If the above example is used, the highest gray level is 8 bits; that is, R, G, and B each have 256 gray levels. Its color is 256X256X256 = 166777216 about 16 million colors. If you want to increase the gray scale to 14 bits, that is, 16384X16384X16384=4.39 billion colors; the refresh rate between the two will also be significantly different.
A. Traditional driver chip (pulse width is 250ns)
The weights are 1/64, 1/32, 1/16, 1/8, 1/4, 1/2, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048
Tfr=25.6usx[6+4095]+5x4us = 105005.6us
Fr = 9.5 Hz
B.SnapDrive driver chip (pulse width is 25ns)
The weights are 1/1024, 1/512, 1/256, 1/128, 1/64, 1/32, 1/16, 1/8, 1/4, 1/2, 1 , 2, 4, 8 , 16, 32, 64, 128
Tfr=25.6usx[10+255]+9x4us=6820us
Fr=146.6Hz
Improvement on Refresh Rate @ 14-bit grayscale + 2-bit Brightness Improvement on Refresh Rate @ 8-bit grayscale + 2-bit Brightness SnapDrive TM Conventional SnapDrive TM Conventional Color 4.39x10 12 4.39x10 12 16.7x10 6 16.7x10 6 Refresh Rate 146.6 Hz 9.5Hz 2264.5Hz 559.7Hz Table 1 shows the comprehensive performance of the traditional driver chip and SnapDriveTM driver chip.
The following is the test conditions and results of the driver chip including SnapDriveTM technology introduced by Taiwan Xunjie Technology. It can be clearly seen from Fig. 1 and Fig. 3 that the output current of the driver chip is still linear output under the minimum OE pulse width, while the conventional driver The chip does not provide a linear output.
Test Conditions:
Vcc=5V, Iout=38.3mA, RL=47Ω, CL=13pF
Reduced distortion rate
For the driver chip with different output current slopes, we use simulation software (HSPICE2007). We get different result distortion rate in terms of distortion rate.
Distortion SnapDrive TM Driver IC 1% Conventional DriverIC 49% Table 2: Distortion Rate Comparison Table
Simulation conditions: traditional driver chip: Ton: 160ns, Tof: 70ns
SnapDriveTM driver chip: Ton: 15ns, Tof: 15ns
Vin : 5V , Iout=20mA , LED equivalent circuit RL: 52Ω, CL: 10pf
OE pulse width is: 250ns
Solve the problem of LED heat and increase the life of LED
As shown in Figure 5, the 50% Dutycycle current output diagram, if the pulse of the current is evenly dispersed in the same time, not only does not affect the output current and the brightness of the LED, it can also avoid LED overheating caused by LED lighting for a long time. And the phenomenon of early decay of life.
Fast response circuit design
The use of a fast-responding driver chip can improve the gray scale and refresh frequency of the LED display; however, the formula according to the inductance effect &D el ta; V = L ?di / dt becomes smaller due to the time t; relatively instantaneous voltage change It is easy to produce a sudden wave. The author has listed several improvements in circuit design for readers' reference:
ΔV : the amount of change in voltage
L: parasitic inductance on the circuit
Di: differential of current
Dt: differential of time
There are a few points that need special attention in circuit design:
1. The PCB is preferably more than 4 layers, and the power supply and the ground are separated by one layer; the shorter the wiring, the better.
2. VLED and VCC add a large voltage regulator to the ground. It is recommended that CP1 and CP2 be 1000~1500uF.
3. VLED and VCC are separated into different power sources.
4. RC circuit can be added to the clock input (Clock) to reduce its peak value and reduce the impact on electromagnetic interference; Rt is recommended
Figure 1: Curve of OE pulse width and output current
Figure 4: Output current distortion rate
Figure 5: Schematic diagram of output current
Figure 6: Driver chip series circuit
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