New LCD Panel Timing Controller and Column Driver Use RSDS Digital Interface to Reduce EMI-Radiated Noise and Lower Power Consumption

National Semiconductor Corporation introduces a chip set for SVGA/XGA TFT LCD panels. The new video IC's incorporate National's power-saving, low-noise Reduced Swing Differential Signal (RSDS) digital interface technology. RSDS is a derivative of the Low Voltage Differential Signal (LVDS) technology used in National's FPD-Link interface chip set - a widely used standard for notebook motherboard to flat panel display. National's new TFT LCD chip set consists of the FPD63310 universal interface SVGA/XGA panel timing controller and the LMC7532 column driver.

"These devices are the first of a kind," said Masaya Higikigawa, Corporate Director and General Manager of the LCD Group at Sharp Corporation. "With the RSDS bus interface, they are designed to work at new lows with regards to both power consumption and EMI-radiated noise. Together, they're key to the upgrade migration toward larger and higher resolution TFT LCD panels. With RSDS technology, all the pieces are now in place to enable the next generation of flat panel displays," he added.

The bus interface between the panel timing controller and column drivers has historically been a major source of EMI and power dissipation inside the panel, due to the common use of TTL level signaling on this bus. However, with National's FPD63310 timing controller and LMC7532 column drivers, RSDS interface signals replace TTL signals on the bus. By reducing the signal swing level and implementing a differential signaling technique, RSDS results in significant reductions in power consumption and EMI levels (versus the TTL bus interface).

"Lowering power and EMI is key to portable applications where TFT LCDs are commonly used for the purpose of extending battery life, reducing weight and thickness, and enabling quicker time to market, while ultimately saving cost," noted Tammy Michel, Marketing Manager for display ICs at National Semiconductor. "We are focused on developing and delivering silicon solutions that address tough customer problems. This chip set does just that."

The FPD63310 timing controller provides the data buffering and control signal generation for the flat panel display, and with integrated RSDS transmitters, drives the LMC7532 column drivers at 130Mb/s with a 65MHz clock. Operating at a 65MHz clock frequency enables a single-pixel system interface, eliminating one of the two pixel busses typically required in TTL-type panels. A narrow 9-pair differential column driver bus minimizes the width of the PCB. In addition, the timing controller is highly programmable, allowing the user to adjust for optimal display quality in real-time by modifying the panelýs timing signals. This programmability enables quicker time-to-market than the gate array approach commonly used today, which takes many weeks for modification. This CMOS device operates from a 3.3V supply.

The LMC7532 column driver receives RSDS data through an integrated RSDS receiver, and converts the 18-bit digital data into analog voltage for the selectable 300 or 309 columns found in SVGA or XGA systems. Use of a switched reference type DAC gives high accuracy with low reference current requirements. The IC consists of an RSDS receiver and demux, registers, latches and output drivers. Typical accuracy is +/-5mV.

This chipset is a different direction for LCD driving and not at all unwelcome. The use of National's RSDR data scheme is a logical extension of LVDS and one that National is, probably, unique in its ability to tap today. The combination should result in the ability to drive larger LCDs more accurately with considerably less EM radiations. It also looks as if the total power consumption of the ICs will result in lower total dissipation for considerably larger displays than we have today. The fact that the low-voltage swings will already considerably reduce radiation and power consumption is compounded by the elimination of one of the buses.

The programmability will allow considerably faster designs than we have today and this is going to be important as we enter a major period of TFT LCD panel development; this is certainly a market where the earliest bird with the largest display and the lowest power consumption wins. The EMI factors are unseen by the consumer but, of course, the costs in correcting radiation problems in a design can be massive.

The LMC7532CT is housed in a TCP (Tape Chip Package) with dual-leads that connect to the panel PCB and glass and is priced at $6.50 in 10,000-piece lots. The FPD63310 is packaged in a 100-pin TQFP and is priced at $8.50 in 1000-piece lots. Both are currently available.