What is LVDS cable
LVDS (Low-Voltage Differential Signaling) is a kind of Differential Signaling technology with low power consumption, low bit error rate, low crosstalk and low radiation, the core of LVDS technology is the use of very low voltage swing high-speed differential transmission of data, can achieve point-to-point or point-to-point connection, the transmission medium can be copper PCB connection, can also be balanced cable.
LVDS (Low Voltage Differential Signaling) is a Low amplitude Differential Signaling technology. It uses a very low amplitude signal (about 350 mv) to transmit data over a pair of differential PCB wiring or balancing cables. It can transmit serial data at speeds of up to thonds of Mbps. Because the voltage signal amplitude is low and is driven by constant current source mode, it only produces very low noise and consumes very little power. In addition, LVDS are not susceptible to common-mode noise because they transmit data in a differential manner.
LVDS was first proposed by National Semiconductor as a National Semiconductor level for high-speed signal transmission. Since then, LVDS has been defined in IEEP 1996.3(approved in March 1996) , primarily for SCI (Scalable Coherent Interface) . The electrical properties of LVDS are defined, and the packet switching codes in SCI protocol are also defined. ANS/EIA/EIA -644(adopted in November 1995-RRB- mainly defines the electrical propertiesLVDSLVDS, the maximum transmission rate and theoretical limit rate are suggested. The commonly mentioned LVDS standard refers to the latter. The 2001 ANS/EIA/EIA -644 standard has been revised and published.
Why LVDS cable was created
With the development of electronic design technology, the interconnection of high-speed signal and the application of broadband channel are increasing day by day. At present, the existing P2P interfaces such as RS-422, RS-485, SCSI and other data transmission standards, due to the inherent limitations in speed, noise, EMI/EMC, power consumption, cost, etc. , make it more and more difficult to meet the practical application. Also with the development of military electronic technology, in the field of space communication, such as tracking and Data Relay Satellite System -TDSSTDSS) , in order to achieve high-speed data relay and ranging, velocity measurement. The problem of high transmission rate and bandwidth must be solved first; in the field of radar application, the emergence of various new radar systems and their applications in different fields such as wideband detection and electronic countermeasure also inevitably face the problem of high-speed data acquisition and transmission; It is becoming more and more outstanding to solve the bottleneck problem of data transmission by using new I/O interface technology. LVDS is becoming the preferred interface standard for broadband high-speed system design because of its inherent characteristics of low voltage, low power consumption and high-speed transmission. At present, LVDS technology is more and more widely used in the field of communication, especially in Base station, large switches and other high-speed data transmission systems, LVDS is playing an irreplaceable role.
What are the technical advantages of LVDS cable
The picture below shows how LVDS works. The source-end driver consists of a constant current source (usually about 3.5 MA, Max not more than 4 Ma) driving a pair of differential signal lines. The receiver itself has a high DC input impedance, so almost all the drive current flows through the 100 ω terminal matching resistance and generates a voltage of about 350 MV at the receiver input. When the source-driven state reverses, the direction of the current flowing through the matching resistor changes, resulting in a high and low logic state change at the receiving end./nIn general, the LVDS receiver input stage also includes an automatic level adjustment circuit, which adjusts the common-mode voltage to a fixed value, it is followed by a Schmitt trigger, and, in order to prevent the instability of the SCDHMITT trigger, the design has some hysteresis characteristics, the Schmitt stage is the difference amplifier.
LVDS is the preferred signal form of high-speed I/O interface to solve the limitation of high-speed data transmission, because it has advantages in transmission speed, power consumption, anti-noise, EMI and so on.
- high speed transmission capability. In the standard of LVDS defined by ANS/EIA/Eia -64, the theoretical limit speed is 1.923 Gbps. The constant current source mode and low swing output mode determine that IVDS has high-speed driving capability.
- low power consumption characteristics. The power consumption of LVDS is only 1.225 MW when the driving current of constant current source is 3.5 Ma and the load (100 ω terminal matching) is only 1.225 MW. The power consumption of LVDS is constant, unlike the dynamic power dissipation of CMOS transceivers relative to frequency. The drive design of constant current source mode reduces the power consumption of the system and greatly reduces the influence of frequency components on power consumption. Although the power consumption of CMOS is lower than that of LVDS when the speed is lower, the power consumption of CMOS will gradually increase with the increase of frequency, and eventually need to consume more power than that of LVDS. Typically, LVDS and CMOS consume roughly the same power when the frequency is equal to 200 msps.
- Low supply voltage. With the development of integrated circuits and the requirement of higher data rate, low-voltage power supply is urgently needed. Reducing the supply voltage not only reduces the power consumption of high-density integrated circuits, but also reduces the internal heat dissipation pressure, which helps to improve the integration. LVDS drivers and receivers do not depend on specific supply voltage characteristics, which determines its dominance in this area.
- strong anti-noise ability. The inherent advantage of the differential signal is that the noise is coupled on a pair of differential lines in a common mode and subtracted in the receiver to eliminate the noise, so LVDS has a strong ability to resist the common-mode noise.
- effectively suppress electromagnetic interference. Due to the opposite polarity of the differential signals, the electromagnetic fields they radiate can cancel each other out. The more tightly coupled they are, the less electromagnetic energy they can release to the outside world, which reduces EMI.
- timing positioning accuracy. Because the differential signal switch change is located at the intersection of the two signals. Unlike the ordinary single-ended signal depends on high and low two threshold voltage judgment, so the process, the temperature of the impact of small, can reduce the timing error, conducive to the effective transmission of high-speed digital signal.
- to adapt to the ground level voltage changes in a wide range. The LVDS receiver can withstand ground voltage changes between the driver and the receiver at least 1v. Due to the IVDS driver’s typical bias voltage of + 1.2 V, the ground voltage change, the driver’s bias voltage, and the sum of the slightly coupled noise at the receiver’s input, the ground is the common-mode voltage relative to the driver. When the swing is less than 400 mv, the common mode range is + 0.2 v ~ + 2.2 V, and then, in general, the input voltage range of the receiver can vary within 0V ~ + 2.4 V. It is because LVDS has the above main characteristics that HyperTransport (by AMD) , Irfiniband (ly Intel) , pCI-Express (by Intel) and other third generation I/O bus standards (3G IO) have adopted low voltage differential signal (IVDS) as the next generation high-speed signal level standard.
What are the use scenarios for LVDS cable
This technology can support high-speed data transmission and is most suitable for communication architecture applications such as base stations, switches, add/subtract multiplexers, etc. , consumer product applications such as set-top boxes and home/enterprise video links, as well as medical ultrasound imaging devices and digital photocopiers, ensure greater flexibility in system partitioning. The system engineer can use LVDS technology to set the analog and digital signal processing section on different circuit boards, and then transmit the digital data output from A/D converter by cable or base board, to ensure greater flexibility in structural design. At present, all kinds of high-speed ADC select LVDS signal as the output format of sampling data, and the output format is parallel output. At the same time, special chips supporting IWDS and other level switching and LVDS speed-down special chips are also emerging, mainly MAXM, Ni and Ti and other foreign companies as representatives./n
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