Mark Hoffman No Comments

The Study of Pulse Recovery Times in GaN LNAs: Part I

The Gallium Nitride (GaN) high electron mobility transistor (HEMT) is well known for its use in microwave and millimeter wave power amplifiers due to its high breakdown voltage and ability to handle high RF power. Recently, GaN technology has also been used to create low noise amplifiers (LNAs) in the microwave region, as the noise properties of GaN are similar to other semiconductor materials, most notably Gallium Arsenide (GaAs). In many microwave systems, LNAs are subject to unwanted high input power levels such as jamming signals. One of the features of LNAs made from GaN is the ability to withstand these input power levels without the need for a limiter, due to the inherent robustness of the device. Indeed, this is one reason GaN LNAs are supplanting their GaAs counterparts, since GaAs LNAs typically require a front-end limiter, which adds to the cost and degrades the performance of the LNA.

Despite the ability to operate without a limiter, GaN LNAs, however, are not completely immune to the effects of high input power. The problem occurs when both a high power jamming signal and the desired signal are input to the GaN LNA, and then the jamming signal is suddenly turned off. Under this scenario, the GaN amplifier does not recover immediately, as there is some residual distortion of the desired signal before normal operation returns. This phenomenon is known as pulse recovery time and is fast becoming an important parameter with regards to LNAs in general. Past researchers have studied pulse recovery times in GaN LNAs, although this work has been limited in scope. One study presented recovery times of less than 30 ns in some amplifiers, but these measurements only utilized a coherent jammer, and the overall number of measurements was limited. A second investigation of pulse recovery time was performed on a GaAs LNA with a limiter. The limiter not only effected the small signal performance, but it also increased the recovery time when high power was applied. Further research has been performed on the degradation of GaN HEMT noise performance after exhibiting DC and RF stress, which can cause forward gate current and damage the gate device. However, this work did not explicitly address pulse recovery times in LNAs. Other papers have similarly analyzed the survivability of GaN amplifiers to high input power overdrive, but again this work offers little understanding of pulse recovery times.

MEASUREMENT TEST SETUP

A setup designed by Custom MMIC uses two signal generators, where the first provides the out-of-band interfering signal at 8.5 GHz, and the second provides the desired continuous wave (CW) in-band signal at 7.5 GHz. The interfering RF signal from #1 is pulsed using a single pole single throw (SPST) switch controlled by a square wave with a low duty cycle. We chose to pulse the signal path, as opposed to the bias circuitry of the interferer amplifier, due to the fast rise/fall time of the SPST, which is on the order of 1.8 ns. Additionally, pulsing the power supply caused high levels of ringing to appear at the output. The interfering signal was amplified by an external power amplifier (PA) and then added to the desired signal with a passive power combiner. We utilized a circulator, terminated in a 20 dB pad and a high power 50 Ohm load, between the combiner and the device under test (DUT) in order to prevent any high power mismatch signal from reflecting back into the PA. The output of the DUT was then attenuated with an additional 20 dB pad, sent through a band pass filter with a pass band of 7.25 to 7.75 GHz, and then input into a digitizing oscilloscope. The filter attenuates the interfering signal to allow for an accurate measurement of the pulse recovery time. Finally, we utilized two different oscilloscopes for the measurement. A Tektronix digital serial analyzer oscilloscope was used to measure the recovery time for the shorter pulse widths, while a Hewlett Packard Digitizing Oscilloscope was used to measure the recovery time when longer pulses were used.

The test procedure consisted of varying the pulse width and the input power of the interfering signal, while keeping the power of the desired signal constant at -10 dBm. A summary of the test conditions including pulse widths, repetition rates, and power levels of the interfering signal are presented in our tech brief . Notably, the input power of the interfering signal was varied between 15 and 27 dBm, with the total energy delivered to the DUT being the important parameter of concern. All measurements with short pulses were performed on the Tektronix oscilloscope, whereas the long pulse measurements were performed on the Hewlett-Packard oscilloscope.

Blog by Custom MMic

Learn more about the study of pulse recovery times in GaN LNA’s.

Mark Hoffman No Comments

pSemi Releases World’s First, Fully Integrated, 8-channel LED Boost

Power Supply in Package (PSiP) Uses a Unique Design Based on a Patented, Two-stage Architecture that Relies on Capacitors to Handle the Bulk of the Power-conversion Work

SAN ANTONIO – APPLIED POWER ELECTRONICS CONFERENCE (APEC) – March 6, 2018 – pSemi Corporation (formerly Peregrine Semiconductor), a Murata company focused on semiconductor integration, introduces the PE23300, the industry’s only fully integrated LED boost power supply in package (PSiP) based on a charge-pump, switched-capacitor architecture that offloads most of the power-conversion work from the inductor to capacitors in the charge pump.

Powering up to eight LED strings at a total power level of up to 10 watts, the PE23300 is designed specifically to power LED backlight arrays in ultra-high-definition (UHD) and high definition (HD) LCD panels for 2-cell and 3-cell narrow-voltage DC notebooks, industrial and automotive displays.

“The PE23300 truly demonstrates pSemi’s power-semiconductor capabilities. The PSiP delivers a unique, two-stage architecture that brings ground-breaking conversion efficiency and small solution size and is packaged with Murata’s advanced, 3D-packaging technology and passive components,” says Stephen Allen, director of strategic marketing at pSemi. “All components required for operation are integrated into a 7.7 x 11.7 millimeter laminate-based LGA package, which is just 1.6 millimeters in height. To achieve this small size, we used a ‘die-in-substrate’ 3D-packaging technology. The low profile is also a result of our two-stage architecture that allows us to use a tiny chip inductor. All of this can be achieved with an efficiency that is on average about 5 to 7 percent higher than the competition, halving the losses in the LED boost.”

Power conversion creates a compromise between size and efficiency: The smaller the solution, the worse the efficiency. This compromise impacts OEMs trying to make next-generation, ultra-compact products, because they need both a very high conversion efficiency and a very small size at the same time. pSemi solves this problem with a novel, two-stage architecture that offloads most of the power-conversion work from the inductor to a virtually lossless charge pump and relies on small, multilayer ceramic capacitors (MLCCs) to do most of the work. As a result, the inductor – usually the largest and tallest component – can be reduced dramatically in size, and traditional wire-wound inductors can be replaced with chip inductors. This patented architecture was first developed by Arctic Sand Technologies, an MIT spin-out acquired by pSemi in March 2017, and commercialized this year.

Beyond the smaller inductor and higher efficiency, this architecture delivers several other key benefits for LED boosts, including full short-circuit protection and a very flat efficiency over the entire load range. Also, efficiency is virtually independent of the output voltage, and this allows more LEDs per string. With fewer strings, efficiency is optimized, and the display-bezel size can be reduced in width. pSemi’s PE23300 features low power dissipation – up to half that of competing products – that improves reliability and supports portable applications’ extensive battery run times.

Product Features

The PE23300 features an input voltage range of 4.5V to 15V DC and powers up to eight strings of LEDs at up to 45V and 40 mA per string.

The PSiP provides full programmability via an I2C interface with settings stored in non-volatile memory or by using GPR pins. Dimming resolution is up to 12-bits resolution with an additional 3-bit dithering and can be either linear/logarithmic analog and PWM dimming or direct PWM dimming for maximum flexibility and resolution. The part features an LED brightness ramp up/down control with programmable ramp rate, linear/logarithmic ramp profiles and phase-shifted PWM dimming among active strings to minimize audible noise.

About pSemi 

pSemi Corporation is a Murata company driving semiconductor integration. pSemi builds on Peregrine Semiconductor’s 30-year legacy of technology advancements and strong IP portfolio but with a new mission: to enhance Murata’s world-class capabilities with high-performance RF, analog, mixed-signal and optical solutions. With a strong foundation in RF integration, pSemi’s product portfolio now spans power management, connected sensors, optical transceivers antenna tuning and RF frontends. These intelligent and efficient semiconductors enable advanced modules for smartphones, base stations, personal computers, electric vehicles, data centers, IoT devices and healthcare. From headquarters in San Diego and offices around the world, pSemi’s team explores new ways to make electronics for the connected world smaller, thinner, faster and better. To view pSemi’s semiconductor advancements or to join the pSemi team, visit www.psemi.com.

(News release by pSemi/March news )

Mark Hoffman No Comments

A Perfect Low Noise Amplifier

Low Noise Amplifiers (LNAs) are a critical component in virtually all radar, wireless communications and instrumentation systems. But while the noise figure (NF) performance is often your primary focus, other microwave system considerations related to performance and size, weight, power and cost (SWaP-C) can be equally, if not more important.  We’ll describe a few other key characteristics that may help you save time during your design cycle, save money during assembly, and even enhance your microwave assembly or subsystem at-large.

1. Input Power Survivability

Specifically in military and aerospace radar and communications applications, where electronic countermeasures (ECMs) may be used to overwhelm a receiver, a receiver must be capable of withstanding high levels of input power for varying intervals of time. Active or passive jamming can cause levels of noise and frequency bursts that couple large amounts of broadband or frequency-selective interference into a receiver. Moreover, in these applications there is often a high-power transmitter in close proximity to the receiver, which can lead to substantial coupling and power ingress into the receiver front end.

A common method to reduce the impact of critically high input powers to a receiver is to include a limiter or circulator on the input of a receiver chain. An unfortunate side effect of adding anything prior to the LNA in the receiver is the degradation of the overall system noise figure. These signal chain additions reduce the sensitivity of the receiver, which may shorten communications range, throughput, radar range and accuracy, and cause delays in acquiring mission critical information. A great 1 dB system noise figure can effectively become 2 dB or more when adding protection circuitry.

It’s thus very important to consider an LNA’s highest input power handling (or input survivability). Most LNAs can handle only 10-15 dBm pulsed on their input, but the highest achievers are now surviving 20 dBm continuously and 23-25 dBm pulsed and can help you eliminate the protection circuitry.

2. Gain Flatness, and Gain Stability over Temperature

Gain flatness across your required band is essential to achieve required inter-symbol-interference (ISI) levels and optimal range performance. As costly equalizers are often employed to compensate for the downward gain slope of typical LNAs, positive gain slope LNAs reduce that need.

Another factor to consider is gain stability over temperature. In applications such as aerospace communications, and SatCom, operating temperature can exceed 180 degrees F of variation within a short time window.

Temperature changes that are significant can affect an LNA by more than just changing the noise figure of the device and system; they can vary the frequency-dependent gain of the LNA. For example, large-phased array antennas may have thousands of TR modules, with many of the modules exposed to a variety of temperature gradients. If the communications system relies on gain stability throughout the TR modules, and the LNAs gain stability is temperature dependent, the system may suffer a significant loss in performance.

3. Supply Voltage and Power Consumption

Properly biasing a MMIC amplifier is critical to achieving adequate device performance. Depending upon the particular LNA design, the biasing circuitry could be composed of a positive and negative biasing circuit with temperature compensation. Some LNA MMICs have the biasing and compensation circuitry built in, but a positive and negative voltage supply must be provided to the exact specification for the biasing network to operate properly.

When designing at a system-level for a large RF or microwave assembly, many different voltage supplies may be required. Certain design constraints may also limit the noise and stability performance of those power supplies, which may impact the practical LNA performance due to limited power supply rejection ratio (PSRR). To avoid this, additional circuitry may be used to condition the voltage supplies for a given LNA MMIC. Each of these circuits and connection points introduces a potential failure mode to the voltage supplies, and thus impacts system reliability. These supply-voltage circuits also consume valuable assembly real estate and power, contribute to the overall size/weight of the assembly, add costs, and of course, consume design and test time.

In order to reduce the infrastructure necessary to integrate a MMIC LNA into a microwave assembly, engineers at Custom MMIC have applied innovative circuit-design techniques. The designs they have implemented, which only require a single positive voltage supply, also enable a wide range of voltage input for even greater flexibility. All of the necessary circuitry to properly bias these LNAs is integrated into the MMIC itself. Ultimately, when your MMIC requires only a single positive supply voltage it reduces your bill-of-material, overall system complexity, failure modes, and overall system SWaP-C.

In mobile platforms, including aerospace and satellite communications, power constraints are also a system-wide limitation that often dictates what solutions can be used. Moreover, for these applications, the power requirements of the components directly lead to the overall size and cost of the power generation circuits, and hence, the total system SWAP-C. An example of this concept is seen with satellite communications. The power required by a phased-array antenna must be generated by solar cells mounted on the satellite, which is one of the largest contributing factors of satellite weight and size. As launching satellites costs thousands to tens of thousands of dollars per kilogram, reducing the weight of a satellite system can directly influence the cost-per-bit of high-speed satellite communication services.

 

What makes for a perfect Low Noise Amplifier (LNA) MMIC for your microwave system? The answer could be right under your noise figure.    (Custommic.com/February News)

Mark Hoffman No Comments

What is a SAW Filter?

Here’s some helpful information about RF/Microwave and SAW filters:

The SAW Filter is a device using surface acoustic wave. A characteristic of the filer is that it can be made small, since Q is high and wavelength is about 5-10 fold of the electromagnetic wave, due to the use of mechanical vibration. Moreover, motion is limited to solid surface, and the filtering function is possible with only the circuit that can control SAW on the surface. Typical SAW filters include: RF SAW Filters, IF SAW Filters, SAW Duplexers, SAW Multiplexer and SAW Resonators.