Power turning point in the hottest LCD and camera

Power turning point in LCD and camera bus scheme

Abstract:

a common development trend today is the serialization of LCD and camera bus, which is to reduce the cost of flexible PCB, save PCB space, and reduce EMI components. However, in terms of serial scheme design, people may think that these serialization schemes will increase additional power consumption because of the increase of devices. This paper will illustrate that if the baseband drive output can be reduced to meet the lower drive requirements of the serializer input, the serialization scheme can reduce the link power consumption. If designers can understand this power turning point of LCD or camera bus, they can reduce the design power consumption

serialization trend:

as more and more functions need to be realized and the shape is more and more complex, people begin to adopt serialization technology to achieve the design goal. Using serialization technology, we can use narrow flexible PCB (FPCB), reduce PCB space, save some unnecessary design of dynamic resistance monitoring system EMI components, and improve reliability by using smaller connectors. Using serialization technology, designers can significantly reduce the number of signal lines sent through FPCB, so as to achieve a smaller and more complex connection design. But even with these benefits, people still have doubts: whether adding additional devices to realize the serialization scheme will increase the power consumption of the system. In view of the strict power consumption limitation of the design, this paper will discuss the authenticity of using serialization technology to reduce power consumption

parallel implementation scheme:

Figure 1 shows a typical parallel scheme

Figure 1 shows a typical parallel scheme

Figure 1: typical parallel scheme

in this architecture, the load of the baseband processor (BP) drive circuit includes the wiring of the main PCB, FPCB, FPCB connector, as well as the wiring on the flip PCB and the final display load. The BP drive circuit must be able to drive the load directly using lvcmos signaling

the display with RGB interface may need up to 24 bits of data, and this pair of wqvga displays will need 8MHz or higher bandwidth after the above project is completed in Harbin, depending on the resolution of the display. The higher the resolution of the display screen, the greater the signal bandwidth required by the display interface

serial scheme:

in the serial display scheme, a pair of devices are placed on the data channels of the main PCB and flip PCB. The serializer is located on the main PCB, which converts the parallel display data into serial data stream and transmits it to the deserializer through FPCB. Depending on the adopted serialization architecture, several serial data signals can be reduced to a pair of differential signals. The deserializer converts the serial data stream into a parallel data stream that drives the display interface (see Figure 2)

Figure 2: serial implementation scheme

there are important differences between the parallel scheme and the serial scheme, and it is these differences that enable the serial scheme to reduce link power consumption. After using a serializer on the main PCB, the requirement of BP output drive circuit is greatly reduced, because the drive load input by the serializer is much lower than that required by the parallel display channel. After using serial interface, BP can also reduce the output voltage and allow the serializer to process the level conversion to the display drive circuit. For example, if the working voltage of the display is 2.7V, BP can reduce the voltage output to the serializer to 1.8V. Then, the deserializer will generate the 2.7V signal required by the display

in addition, most serial schemes use differential signaling protocol, similar to low-voltage differential signaling (LVDS). This signal can greatly reduce the voltage amplitude required to transmit data through FPCB, and also reduce the EMI of the signal link. By reducing the signal amplitude and canceling the double shielded FPCB due to the reduction of EMI in the serial stream, the serial scheme can reduce power consumption

power turning point:

for a given application, the turning point of using serial scheme to save power consumption than using parallel scheme is the power turning point. For our example, using the empirical estimation of system parameters, we can approximate the power turning point by comparing the display link power consumption of the serial and parallel data paths. Dynamic power consumption can be obtained from the following equation:

in this equation:

C = payload capacitance of the driven link

V = voltage amplitude of the display signal

fclk = display data channel bandwidth

afactor = effective activity factor of the display signal (average rate of data bit level conversion)

nbits = display channel data bit width

Figure 3: dynamic power calculation

in these parameters, Except for C and afactor, most of them have been discussed in this paper. C is related to the system. In terms of parallel scheme, C can be taken as 80pf to estimate typical applications including PCB wiring, flexible connectors, FPCB, esd/emi components and display drive circuit input load. Afactor is related to data and varies greatly with different applications, but in this calculation, it is assumed to be 50%

using these parameters and the equation in Figure 3, the power consumption of the parallel scheme is calculated to be 29MW according to the following parameters

c = 80pf

v = 2.7v

fclk = 8mhz

afactor = 50%

nbits = 24

for the serial scheme, the power consumption calculation is slightly different. The method adopted here is to calculate the power consumption of BP driven serializer and the power consumption of deserializer driven display drive circuit when starting the construction of medium and heavy plate phase 2 project with Nanshan aluminum in a timely manner

according to the following parameters, the power consumption of BP driven serializer is 0.5MW

c=3pf

v=1.8v

fclk=8mhz

afactor=50%

nbits=24

it can be seen that due to the reduction of BP output load, the voltage and driving current of BP IO can be reduced, thus greatly reducing power consumption

using the same method, the power consumption of the deserializer drive display drive circuit is calculated to be 14.5mw according to the following parameters

c=40pf

v=2.7v

fclk=8mhz

afactor=50%

nbits=24

according to this calculation, the power turning point of this example is 14MW, that is, the difference between the parallel power consumption and the parallel part power consumption of the serial scheme. This power turning point determines the threshold at which the serial link power consumption reaches balance. For this example, the power consumption index of the current serial scheme is less than 20MW. This means that the design power consumption of increasing serialization processing is only increased by less than 6MW. If the power consumption is further reduced, such as canceling some passive components commonly used in the case of the parallel side for most of the use of high molecular polymers, the serial scheme can truly reach the power turning point

through the fine implementation of serialization, the power consumption of the display data path can be further reduced, so as to improve the power turning point. This can include the cancellation of some EMI components and ESD protection devices on the display data path, because in the serial scheme, the serializer and deserializer pair can provide ESD protection against current transients on the FPCB for BP and display drive circuit

summary:

serialization technology has been increasingly applied to today's design. Serialization technology is mainly used to save space, but people often think that it will significantly increase the power consumption of the system. This paper dispels this doubt and clarifies the principle of serialization technology to actually reduce power consumption. Current serialization solutions are narrowing the gap between serial power consumption and power turning point. This means that in addition to other benefits brought by serialization technology to the design, the link power consumption of the serial solution can be reduced, so the power consumption of the whole system can be reduced