The ut54lvds031lv quad driver is a quad cmos differential line driver designed for applications requiring ultralow power dissipation and high data rates. The max14979e is optimized for highspeed differential switching applications. The transmitter output vob and voa are the outputs coupled to the transmission lines. The current switch constituted by m1, m2, m3, and m4 is controlled by d and d. Lvds, cml, ecldifferential interfaces with odd voltages ee. The lvds output consists of a current source nominal 3. Lvds, cml, ecldifferential interfaces with odd voltages. Hi, i am designing a lvds tx, but i dont know how to simulate the output impedance. For common mode impedance, i connect an idc source dc current 0, ac magnitude 1a in serial, and the output impedance is about 1. An10066 lvds output with 600 mv to 1200 mv swing sitime. Lvds output to cml input interfacing from lvds to the hotlink ii is straightforward.
What is the fanout capability of the cmos lvds and lvpecl. Engineers at national semiconductor in santa clara, calif. Low voltage differential signaling lvds is the most common differential transmission system, and it is used for. In addition, four switch transistors, m2, m3, m4, and m5 were carefully designed so that their impedances will be negligible relative to the output impedance of the driver. Vos figure 1 25 mv output high voltage voh figure 1 1. Differential clock translation microchip technology. With the desired receiver input voltage defined as v receiver, the pulldown resistor is calculated using equation 1 along with the effective schematic in figure 2, page 2.
Lvds driver output structure lvds 1 is a highspeed digital interface suitable for many applications that require low power consumption and high noise immunity. The device is ideal for lowvoltage differential signal lvds and lowvoltage, positive emittercoupled logic lvpecl switching applications. Texas instruments provides a complete portfolio of lowvoltage differential signaling devices for all your design needs. Both the drivers and the receiver feature activeterminated ports that eliminate the. A reclockercable driver connects directly tothe outputs of the crosspoint switch to drive the signals acrosscables. A lowpower 5gbs currentmode lvds output driver and. Design of a lowpower cmos lvds io interface circuit. The lvds driver is intended to be loaded with a 100ohm load connected across the pair. C l includes all probe and jig capacitances figure 4. Max92 programmable, highspeed, multiple inputoutput. Lvds application and data handbook texas instruments. Diodes lvds low voltage differential signaling devices solve todays high speed io interface requirements with high performance 5 v, 3. Tdk emc technology practice section emc countermeasures.
Max92 programmable, highspeed, multiple inputoutput lvds. Introduction to lvds, pecl, and cml maxim integrated. The max92max94max95 highspeed, multipleport, lowvoltage differential signaling lvds crossbar switches are specially designed for digital video and camera signal transmission. Using lvds to compensate for impedance discontinuities in a digital video router design may 30. Lvds uses a 100ohms balanced termination resistance at the receiver, which for a differential signal is equivalent to each line having a 50ohm unbalanced load. Understanding lvds for digital test systems national instruments. The differential output impedance is typically 100 refer to table iii for other output specifications. Refer to figure 1 for a representation of an lvds driver stage. The reason of this data rate achieving is because of its low output voltage swing, which results in a fast switching slope rs422 has a voltage swing of two volts, which results in a slope of around 2ns, but lvds only has 350 mv resulting in a slope of around 0. The footprint of the ut54 lvdm031lv is the same as the industry standard quad differential rs422 driver. The stc104 is a packet routing switch for ieee 55 ds packets. All input pulses have frequency 50 mhz, tr or tf 500 ps note b. The full circuit, including an lvds receiver, is shown in figure 2. These switches have a wide bandwidth, supporting data rates up to 840mbps.
To get full impedance matching of the transmission line and termination resistor. Help how to simulate output impedance of a lvds driver. Lvds input to lvds driver propagation delay and transition time circuit figure 5. For differential outputs, place the surfacemounted r. A common backplaneconnects the signals from the input card to the switch card for outputto the desired destination channel. Evaluation kit available lowjitter, 10port lvds repeater. The driver tends to be a currentmode driver, driving the balance interconnect cable to a load consisting of the termination resistor and the receiver.
The equivalent circuit structure of the lvds physical layer is shown in figure 1. The driver output impedance is used to terminate reflections from the receiver so. Ut54lvdm031lv pinout ut54lvdm031lv driver 16 15 14 12 11 10 9 vdd. A current mode driver, has a high output impedance and supplies a constant current for a range of loads a voltage mode driver on the other hand supplies a constant voltage. You can easily generate lvds signals using two dio channels to generate the two ends of the differential signal. Measurements show that the proposed lvds driver can be used at frequencies as high as 2. Using a positive feedback technique, the driver achieves ultra low power operation while maintaining the proper internal chip impedance required for matching the. As can be seen by the topology of the lvds output driver in figure 2, the circuit operation results in a fixed dc load current on the output supplies. Also, a lowsignal current version of the lvds driver working with lower supply voltage is proposed along with a compatible differential currentmode receiver.
Lvds data transmission catches on in defense and satellite applications. Therefore, the majority of driver current flows across the 100. Design of a lowpower cmos lvds io interface circuit 1102 fig. Us6900663b1 low voltage differential signal driver circuit.
Voh and vol are the output voltages of the driver with respect to ground. Lvds outputs can conceivably drive multiple loads, but this is not usually part of the language of lvds. The differential output impedance is typically 100 refer to. Differential impedance finally made simple eric bogatin president bogatin enterprises. Lvds low voltage differential signaling provides a means of sending data.
The current diverted by the impedance circuit may be compensated for by increasing the source current from the programmable current sources. Differential signaling doesnt require differential impedance. Resistor r1, in series with the on resistance of the fets, determines the source impedance of the driver. Using lvds to compensate for impedance discontinuities in. Lvds outputs use differential signals with low voltage swings to transmit data at high rates. Passive switch provides lvds signal routing electronic design. Lvds data outputs for highspeed analogtodigital converters. Embodiments of the present invention relate to a low voltage differential signal driver lvds circuit which comprises a current source, logic controlled switches for controlling the drivers output, an electronic load circuit coupled across the circuit, and a commonmode resistor feedback circuit coupled across the circuit, in parallel with the rc load, for tuning the drivers impedance. Interface lvds signals using pericom switches pi3v512.
In this work, a novel circuit topology for a lowvoltage differential signaling lvds output driver with reduced power consumption is proposed. Pecl is a low impedance output, and is designed to drive 50 ohm loads, to allow it to drive unbalanced terminated 50 ohm interconnects. This avoids current spikes that would be seen in a typical cmos output driver when the output logic state transitions. In addition, the max94max95 provide pins to set switch routing. In the driver, a current source limits output to about 3 ma, and a switch box steers the current through the termination resistor. The power consumption at the load can be calculated using the power equation, p i 2 r, which states that power is equal to electrical current squared times resistance. A high speed, low power consumption lvds interface for. Differential signaling doesnt require differential impedance or, how to design a differential signaling circuit that title may seem like a complete contradiction to the wisdom written in many design documents describing how to route differential pair signals. A high speed, low power consumption lvds interface for cmos. Passive switch provides lvds signal routing electronic. Xilinx xapp520 interfacing 7 series fpgas highperformance i. Switching lvds graphics in a laptop computer application. Ansitiaeia6441995 is the generic physical layer standard for lvds.
Differential signaling doesnt require differential. Typically, lvds devices are divided into four categories driver, receiver, transceiver, and buffer. Ds90lv047a 3v lvds quad cmos differential line driver. Low voltage differential signaling lvds is the most common differential transmission system, and it is used for many devices that require highspeed transmission because of its generalpurpose properties. Index termscmos integrated circuits, currentmode logic cml, lowvoltage differential signaling lvds, output. Closely matching the impedance of this termination resistor with the. Us6900663b1 low voltage differential signal driver. Both the drivers and the receiver feature activeterminated ports that eliminate the need. Lowswing vm driver impedance control 24 a linear regulator sets the output stage supply, v s termination is implemented by output nmos transistors to compensate for pvt and varying output swing levels, the predrive supply is adjusted with a feedback loop the top and bottom output stage transistors need to be sized. Lvds differential line driver texas instruments lvds. Using differential io lvds, sublvds in ice40 lphx devices.
Today ill introduce lvds technology, cover lvds operations, and clarify differences between lvds and other interfaces. The digital video or camera signal can go through the switches from an input port to one or multiple output ports. The device is designed to support data rates in excess of 400. The pulldown resistor can be determined by knowing the output driver impedance resistance and output drive voltage vcc. A comparison of cml and lvds for highspeed serial links. The programmable lvds output driver may also include an impedance circuit for adjusting the output impedance of the output driver, while only diverting a small amount of source current. Jun 24, 2019 the currentmode driver of lvds provides a constant 3. When choosing board ethernet connectors, i see that there are all sorts of types out there.
Vod figure 1 25 mv offset commonmode voltage vos figure 1 0. Because the max4889 can switch between two lvds sources to a single destination, it is an ideal choice of switch for a laptop design. Circuit operation can be explained as follows also. An lvds output voltage can switch from one logic state to the opposite in 260 ps and. Differential clock translation lvpecltolvds translation placing a 150 resistor. Tdk emc technology practice section emc countermeasures of. Interfacing to lvds with the ni 655x digital waveform. Lvds data transmission catches on in defense and satellite. The virtexe lvds line driver behaves like a current source in parallel with a 50. Embodiments of the present invention relate to a low voltage differential signal driver lvds circuit which comprises a current source, logic controlled switches for controlling the driver s output, an electronic load circuit coupled across the circuit, and a commonmode resistor feedback circuit coupled across the circuit, in parallel with the rc load, for tuning the driver s impedance. Lvds operates at low power and can run at very high speeds using inexpensive twistedpair copper cables. To permit this possibility, a simple solution would be to add a switch to the design that would select either internal graphics or the lvds output of the addin card.
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