Nowadays, laterally diffused metal oxide semiconductor (LDMOS) transistors are widely used for RF Power Amplification and in many applications. A simplified circuit of an LDMOS amplifier bias circuit is shown in the schematic diagram above. The DC Bias on these amplifiers is set by applying a DC voltage to the gate (VGS) and by monitoring the Drain current (IDD). Ideally, this IDD will be constant over temperature, but since the VGS of LDMOS amplifier devices varies with temperature, some type of temperature compensation is required.
The ISL21400 features a precision voltage reference combined with a temperature sensor whose output voltage varies linearly with temperature. The precision 1.20V reference has a very low temperature coefficient, and its output voltage is scaled by an internal DAC (VREF) to produce a temperature stable output voltage that is programmable from 0V to 1.20V. The output voltage from the temperature sensor (VTS) is summed with VREF to produce a temperature dependent output voltage. The maximum voltage supply of the ISL21400 is 5.5V, and the LP2950 voltage regulator drops the LDMOS voltage to 5.5V for the ISL21400 supply. An LC filter is then added to the output of the voltage regulator to ensure no RF energy present on the supply line. The ISL21400 can be tied to a microcontroller or to any I/O connector for PC control and programming.
The RFPA bias control using the ISL21400 is very straightforward. The RFPA uses the Freescale AFT21S140W02GSR3. LDMOS are useful devices for many applications including commercial FM broadcasting and TV power transmitters, cellular and paging communication systems, and military RF and microwave hand-held transceivers.
LDMOS Transistor Bias Control in RF Power Amplifiers – [Link]
by R. Colin Johnson @ eetimes.com:
PORTLAND, Oregon — Scientists trying to fulfill the 80-year-old dream of Nobel laureate Eugene Wigner, recently discovered how to place crystalline lattices of pure electrons in the bottom of a silicon-encased quantum well. The resulting material promises electron mobility more than 200 times greater than that of graphene and more than 1,700 times that of crystalline silicon.
So far, the work is still at the level of fundamental physics, but if researchers make the kind of advances they anticipate they could open a door to significant applications in semiconductors.
Scientists Pursue Super-Fast Material – [Link]
by w2aew @ youtube.com
The Vbe Multliplier circuit, also known as an Amplified Diode or Adjustable Diode, is a useful circuit that allows you to set a user desired voltage drop without using a series combination of diodes or zeners. This video describes and demonstrates how this circuit works, and shows a few applications where it is used. It is commonly used to set the bias on a low-impedance push-pull output stage of an amplifier. All transistors shows are typical general purpose devices like the 2N3904/2N3906. The scope is being used as a simple curve tracer in the first part of the video.
Basics of a Vbe Multiplier: what it is, how it works & where it is used – [Link]
by Einar Abell @ edn.com:
This Design Idea gives two versions of an indicator light that changes from green to red as a battery discharges. There are many circuits that do this sort of thing, but all the ones I have seen are too complex and costly for my taste. This DI shows a method that uses an absolute minimum of low cost parts: a dual-color LED and four other parts.
Voltage indicator transitions between colours – [Link]
by R. Colin Johnson @ eetimes.com:
A new type of transistor harnesses a new effect–called the quantum spin Hall effect — to create a topological field effect transistor (TFET) according to a Massachusetts Institute of Technology (MIT) researcher who recently moved to the newly formed Department of Materials Science and Engineering at Texas A&M University where the Texas Advanced Computer Center (TACC) confirmed the researcher’s results.
“We found that when deposited in a flat sheet just three atoms thick, our crystalline lattices exhibited a new electronic effect we call the quantum spin Hall effect,” professor Xiaofeng Qian told EE Times.
Transistors Prelude Quantum Computers – [Link]
by Graham Prophet @ edn-europe.com:
Researchers at IMEC have produced an 8-bit microprocessor that runs at 2.1 kHz. That is not a typing error for GHz; 2.1 kHz is a breakthrough speed in this instance because the transistors that make up the processor’s logic are entirely fabricated in low-temperature organic materials. Possible areas of application include high-volume printing of RFID tags.
Belgium’s Holst Centre, IMEC and their partner Evonik have fabricated a general-purpose 8-bit microprocessor using complementary thin-film transistors (TFTs) processed at temperatures up to 250 °C, compatible with plastic foil substrates. The “hybrid” technology integrates two types of semiconductors – metal-oxide for n-type TFTs (from materials companies iXsenic and Evonik) and organic molecules for p-type TFTs – in a CMOS microprocessor circuit, operating at a clock frequency unprecedented for TFT technologies of 2.1kHz. The results were published online in Scientific Reports.
by Ransom Stephens @ edn.com:
Moore’s Law, famous for predicting the exponential growth of computing power over 40 years, comes from a simple try-fail/succeed model of incremental improvement. The predictive success of Moore’s Law seems uncanny, so let’s take a closer look to get an idea of where it comes from.
Moore conceived his law for computational power but Moore’s-like growth laws permeate human endeavor—a fact that had never occurred to me until I went to a presentation by Lawrence Berkeley National Lab energy researcher, Robert van Buskirk. He showed several technologies that improve according to Moore’s law, but with different timescales than the original. You can read his paper here, notably co-authored by Nobel Laureate and former Secretary of the Department of Energy, Steven Chu.
Moore’s Law extends to cover human progress – [Link]
Two-dimensional (2D) materials such as molybdenum-disulfide (MoS2) are attracting much attention for future electronic and photonic applications ranging from high-performance computing to flexible and pervasive sensors and optoelectronics. But in order for their promise to be realized, scientists need to understand how the performance of devices made with 2D materials is affected by different kinds of metal electrical contacts.
Researchers in PML’s Semiconductor & Dimensional Metrology Division, in collaboration with researchers from George Mason University, compared silver and titanium contacts on MoS2 transistors to determine the influence of the metal–MoS2 interface.
Scientists discover a better metal contact that improves two-dimensional transistor performance – [Link]
Alex Lidow @ edn.com:
For the first time in 60 years, a new higher-performance semiconductor technology is less expensive to produce than the silicon counterpart. Gallium nitride (GaN), has demonstrated both a dramatic improvement in transistor performance and the ability to be produced at a lower cost than silicon. GaN transistors have unleashed new applications as a result of their ability to switch higher voltages and higher currents faster than any transistor before. These extraordinary characteristics have ushered in new applications capable of transforming the future. But this is just the beginning.
GaN field effect transistors (FETs) are now available as discrete transistors and as monolithic half-bridges, with performance 10 times better than the best commercial silicon MOSFET. But what happens when many devices are integrated to create a system on a single chip? What happens when the performance of that chip is 100 times better than silicon?
GaN technology will transform the future – [Link]