App note: Voltage generating circuits for LCD contrast control


Another application note from Hantronix, Inc. on simple to digitally controlled efficient power supply for LCD display contrast. Link here (PDF)

Many LCD display modules require a negative or positive voltage that is higher than the logic voltage used to power an LCD. This voltage, called Vl, Vee or the bias voltage, would require a second power supply in the application device. If this power source is not available the LCD bias voltage must be generated from an existing voltage, either the logic voltage (+3.0-+5v) or a battery. This application note describes circuits for generating either a negative or positive LCD bias voltage from such a voltage source.

The LCD bias voltage is used to power the circuits that drive the LCD glass. This voltage sets the contrast level of the LCD. Since any changes in this voltage will cause a visible change in the contrast of the LCD it must be regulated to better than about 200mV. Any noise or ripple on this signal may cause visible artifacts on the LCD so they must be kept below about 100mV.

App note: An explanation of LCD viewing angle


An application note from Hantronix, Inc. on LCD viewing angles and how it influences the selection of the right LCD for your application. Link here (PDF)

LCD displays have a limited viewing angle. They lose contrast and become hard to read at some viewing angles and they have more contrast and are easier to read at others. The size of the viewing angle is determined by several factors, primarily the type of LCD fluid and the duty cycle. Because the viewing angle tends to be smaller than most people would like, a bias is designed into the module at the time it is manufactured. This means the nominal viewing angle is offset from the perpendicular by some amount. Several versions of the LCD module are then offered with this bias set to different angles or positions to accommodate as many applications as possible. The term “bias angle” is often used erroneously with the term “viewing angle”.

App note: High-speed input clock issues


Clock jitter are a big issue in high-speed ADC, here’s an application note from e2V to guide users deals with these problems. Link here (PDF)

The e2v converters family addresses the high-speed market in the field of ADCs as well as DACs, with frequencies operating in the GHz range. Such high-speed devices require high-speed clock signals, which are usually subject to noise and wich users are not used to deal with. As a matter of fact, the clock signal integrity is one of the main factor to be taken into account for proper operation of an ADC.

High-speed ADCs require a low phase noise clock (namely a low jitter clock) in order to limit the dynamic performance degration caused by noise on the clock. Event though many manufacturers offer crystal oscillators with the right jitter characteristics, only a few are able to generate clocks in the GHz range.

These two issues are addressed in this paper, which intends to help the user understand the jitter phenomenon and design a proper clock with the right performance.

App note: Power factor correction using the IRS2500


Drop in replacement power factor correction chip IRS2500 from International Rectifier. Link here (PDF)

Many offline applications require power factor correction circuitry in order to minimize transmission line losses and stress on electrical generators and transformers created by high harmonic content and phase shift. Appliances often incorporate switching power supplies (SMPS) which include capacitive filter circuitry followed by a bridge rectifier and bulk capacitor supplying a load. Without power factor correction circuitry a SMPS draws a high peak current close to the line voltage peak and almost no current over much of the cycle, resulting in a power factor of around 0.5 and a high total harmonic distortion. Power factor correction circuitry is added which enables the appliance to draw a sinusoidal current from the AC line with negligible phase shift and very low harmonic distortion. This allows optimization of the load seen by the power grid such that power can be supplied without creating additional conductive losses in transmission lines or additional burden on transformers and generators. Costs to electricity providers are therefore reduced, which are hopefully passed on to the consumer.

App note: Auto-zero amplifiers ease the design of high-precision circuits


An application note from Texas Instruments on new chopper amplifers superiority over old design chopper amps. Link here (PDF)

This article shows that the auto-zero calibration technique is very different from the chopper technique and is one that, when implemented through modern process technology, allows the economical manufacturing of wideband, high-precision amplifiers with low output noise.

App note: Transmitting SXGA video signal through 1kft (300m) CAT-5 cable


An app note from Intersil on utilizing CAT-5 cable for SXGA video transimission. Link here (PDF)

The goal of this application note is to present the most current design methods for transmitting high bandwidth SXGA video signal over long distances of CAT-5 cable (300m or more). The enormous cost benefits of CAT-5 cable will also be discussed; for instance, the average cost of a 100m of CAT-5 cable is $20 while the average cost of a 100m of Coax Cable could easily exceed $240. Furthermore, wiring is reduced from a bulky hard to manage bundle of 3 cables to 1 easily pulled cable. Additionally, CAT-5 cable has a 4th twisted pair available, which can be used for KVM signal, audio, timing or control signal transmission.

App note: Thermal behavior of small-signal discretes on multilayer PCBs


App note from NXP Semiconductors about multilayer PCB as additional heatsink for flat SMD components mostly power transistors to dissipate heat. Link here (PDF)

This application note illustrates how to improve the power dissipation of discrete components by using multilayer PCBs. It focuses on the impact of using larger copper areas to improve the thermal behavior of applications.

App note: Enhancing cellphone battery performance during GSM pulses through the use of a parallel supercapacitor


Low ESR and ESL supercapacitor paralleled to cellphone batteries can react more quickly to the demanding power required by GSM pulses. A great appnote read from AVX, link here (PDF)

With the constant addition of features and functionality, battery life and reliability are becoming increasingly vital to those who rely on their smartphones. The transmission signal requires quick pulses of current from the battery, potentially causing the instantaneous voltage of the battery to drop below the phone’s minimum voltage of operation. This may cause the power to the battery to be temporarily interrupted. A series of tests were performed on multiple battery chemistries to determine the beneficial effect of placing an AVX supercapacitor in parallel with the battery, to improve the life of the battery as well as the quality of power provided from it.

App note: Projection with LED light sources


LEDs are now mostly used in light projection systems due to their low power requirements, long life and robustness. Here’s an app note from OSRAM for proper integrations on these projection LEDs. Link here (PDF)

This application note provides insights into the use of LED light sources for projection applications. An overview of LED projection systems and their benefits is presented, along with a summary of OSRAM Opto Semiconductors LEDs suitable for these applications. Finally, fundamental design issues related to the use of LEDs in projection modules are addressed.

App note: Potting protection for outdoor LED video walls and signs


LED signs and large LED video panels are always subjected to harsh environment resulting to corrosion to their pcb mountings, here’s an app note from OSRAM about potting these LED panels for protection. Link here (PDF)

This note provides basic information about the potting of flat SMT LEDs in video wall and signage applications. Thereby details on material in use, examples of suitable equipment and the process are presented and described. Additionally, the note gives a short intro into video walls with a typical setup, varying LED type system effects and general challenges. Finally, the results of selected environmental tests are presented, to demonstrate their impact and the aptitude of potting protection method.