X-bit labs

X-bit’s Guide: Contemporary LCD Monitor Parameters and Characteristics (page 22)

Category: Other

by Oleg Artamonov

[ 10/26/2004 | 02:58 PM ]

IPS Matrices

The IPS technology was developed by Hitachi in 1996 to solve the two plagues of TN-matrices: small viewing angles and low-quality color reproduction. The name – In-Plane Switching – comes from the crystals in the cells of the IPS panel lying always in the same plane and being always parallel to the panel’s plane (if we don’t take into account the minor interference from the electrodes). When voltage is applied to a cell, the crystals of that cell all make a 90-degrees turn. By the way, an IPS panel lets the backlight pass through in its active state and shutters it in its passive state (when no voltage is applied), so if a thin-film transistor crashes, the corresponding pixel will always remain black, unlike with TN matrices.

The figure above shows that IPS matrices differ from TN ones not only in the structure of the crystals, but also in the placement of the electrodes – both electrodes are on one wafer and take more space than electrodes of TN matrices. This leads to a lower contrast and brightness of the matrix.

The original IPS technology became a foundation for several improvements: Super-IPS (S-IPS), Dual Domain IPS (DD-IPS), and Advanced Coplanar Electrode (ACE). The latter two technologies belong to IBM (DD-IPS) and Samsung (ACE) and are in fact unavailable in shops. The manufacture of ACE panels is halted, while DD-IPS panels are coming from IDTech, the joint venture of IBM and Chi Mei Optoelectronics – these expensive models with high resolutions occupy their own niche, which but slightly overlaps with the common consumer market. NEC is also manufacturing IPS panels under such brands as A-SFT, A-AFT, SA-SFT and SA-AFT, but they are in fact nothing more than variations and further developments of the S-IPS technology.

S-IPS panels have gained the widest recognition, mostly due to the efforts of another joint venture LG.Philips LCD, which is outputting rather inexpensive and high-quality 19” and 20” matrices. The price – you can buy a 19” LG L1910S monitor on an S-IPS panel of the latest generation for slightly more than $600 – is an important achievement since IPS matrices have long been the costliest, and this fact impeded their development greatly.

Besides the high price, the response time was among the serious drawbacks of the IPS technology – first panels were as slow as 60msec on the “official” black-to-white-to-back transitions (and even slower on gray-to-gray ones!). Fortunately, the engineers dragged the full response time down to 25 milliseconds lately, and this total is equally divided between pixel rise and pixel fall times. Moreover, the response time doesn’t greatly grow up on black-to-gray transitions compared to the specification, so modern S-IPS matrices can challenge TN ones in this parameter.