"The promotion of performance, miniaturization, and higher frequency is being challenged the limitations of two key antenna connecting components of wireless systems: power amplifier (PA) and low noise amplifier (LNA). Make 5G a reality effort, and PA And LNA uses the use of VSAT terminals, microwave radio links, and phase-controlled radar systems to promote this transformation.
The requirements for these applications include lower noise (for LNA) and higher energy efficiency (for PA) and running at higher frequencies above 10 GHz. To meet these increasing demands, LNA and PA manufacturers are stepping from conventional allish silicon processes to gallium (Gaas) for LNA and gallium nitride (GaN) for PA.
This article will introduce the role and requirements of LNA and PA and its main features, and then introduce typical GaAs and GaN devices and matters that should be kept in mind when designing these devices.
Sensitive effect of LNA
The role of LNA is to obtain extremely weak uncertain signals from antenna, which is usually a signal of microastvolta level or less than -100 dBm, then amplifying the signal to a more useful level, typically about 0.5 to 1 V ( figure 1). Specifically, 10 μV of 10 μV in a 50 Ω system is -87 dBm, 100 μV equal to -67 dBm.
Such gain can be easily implemented using modern electronic technology, but the problem will be far less simple when adding various noise in a weak input signal. The enlargement advantage of LNA will completely disappear in such noise.
Note that LNA works in a world full of unknown. As the front end of the transceiver channel, the LNA must capture and enlarge the low voltage signals of the related bandwidth and the low voltage signals and the related random noise caused by the antenna. In the signal theory, this is called unknown signal / unknown noise puzzle, which is the most difficult part in all signal processing challenges.
The main parameters of LNA are noise factors (NF), gain, and linearity. Noise comes from the heat source and other noise sources, the noise coefficient is 0.5 - 1.5 dB. The typical gain of the single-stage amplifier is between 10 - 20 dB. Some design uses a higher gain and low NF level plus a higher level of cascaded amplifier, which may reach a high NF, but once the initial signal has "increase", this is not so much important. (For details on the LNA, noise, and RF receivers, see the "Low noise amplifier to maximize the sensitivity of the receiver" in Techzone.)
Another problem with LNA is non-linearity because synthetic harmonics and intermodulation distortions have deteriorated the received signal quality, which makes signal demodulation and decoding more difficult when bit error rate (BER) is quite low. Usually used three-order interchange points (IP3) as a characteristic parameter of linearity, the nonlinear product caused by the third-order nonlinear item is associated with signals amplified in linear mode; the higher the IP3 value, the linearity of the amplifier performance The better.
Power consumption and energy efficiency are usually not a primary problem in LNA. In essence, most of the LNAs are equivalent to power consumption and power consumption between 10 - 100 mA, which provide voltage gain to the next level, but does not deliver power to the load. In addition, only one or two LNAs are used in the system (the latter commonly used in the multi-function antenna design of the ports such as Wi-Fi and 5G), so the significance of energy saving by low power LNA is not large.
In addition to operating frequency and bandwidth, various LNAs are relatively similar. Some LNAs also have gain control functions, so it is possible to cope with the wide dynamic range of the input signal without overload, saturation. In mobile applications where the base station to the mobile phone channel loss range, the input signal intensity varies so broadly, even if the single connection cycle is true.
The route of the input signal to the LNA and the specifications from its output signals are as important as the components themselves. Therefore, designers must use complex modeling and layout tools to achieve all of LNA's total potential performance. Due to poor layout or impedance matches, high-quality components may be easily deteriorated, so it is necessary to use the Smith circle provided by the supplier, and support the reliable circuit model of simulation and analysis software.
For these reasons, almost all high-performance LNA vendors operating within GHz ranges provide an evaluation board or verified printed circuit board layout because each aspect of the test setting is critical, including layout, connector, ground , Bypass and power. Without these resources, designers need to waste time to assess the performance of components in their application.
One representative of LNA based on GaaS is HMC519LC4TR. This is a 18 to 31 GHz Phemt (Fig. 2) from Analog Devices (Fig. 2). Such a non-lead 4 × 4 mm ceramic surface mount package provides 14 dB small signal gain, and a low noise coefficient of 3.5 dB and a high IP3 of + 23 dBm. The device can extract 75 mA from a single +3 V power source.
From a simple functional block diagram to multiple external capacitors with different values and types require a design process, providing appropriate RF bypass, with low parasitic effects on three power rails, specified as VDD (Figure 3).
According to this enhancement schematic, the evaluation board is generated, and the layout and BOM, including non-FR4 printed circuit board materials (Fig. 4 (a) and 4 (b)).
MacM Maal-011111 is a GaAs LNA for higher frequencies that support 22 to 38 GHz operations (Figure 5). The device provides 19 DB of small signal gain and 2.5 dB noise factor. The surface of this LNA is a single-stage device, but there is actually three levels in the inside. The first level is optimized for minimum noise and medium gain, and the subsequent level provides additional gain.
Similar to Analog Devices, Maal-011111 only requires only one low voltage power supply, and the size is only 3 × 3 mm, which is very small. Users can adjust and trade out certain performance specifications by setting offset (power) voltages between different values between 3.0 and 3.6 V. It is recommended that the board layout shows the key printed circuit board copper sizes needed to maintain appropriate impedance matching and ground performance (Figure 6).
PA drive antenna
Contrary to the signal capture challenge of the LNA difficult, PA is the relatively strong signal from the circuit, has a high SNR, and must be used to improve the signal power. All general-purpose coefficients associated with signals, such as amplitude, modulation, waveform, duty ratio, etc. This is the most easily responded to the known signal / known noise quadrature in the signal processing chart.
The main parameters of PA are power output at the correlation frequency, and the typical gain is between +10 to +30 dB. Energy efficiency is another key parameters secondary in the PA parameter, but use models, modulation, duty cycle, allowing distortion, and other aspects of the drive signals to make any energy efficiency assessment complicated. The energy efficiency of PA is between 30 and 80%, but this is largely determined by a variety of factors. Linearity is also the key parameters of PA, which is determined using an IP3 value as in LNA.
Although many PAs use low power CMOS technology (up to about 1 to 5 W), in recent years, other technical industries have developed mature and widely used, and considering the key indicators that will function as battery life and heat dissipation. This is especially true in the case of high power levels. In the case where several watts or higher power are needed, Gallium nitride (GaN) has better energy efficiency at higher power and frequency (typically 1 GHz). In particular, when considering energy efficiency and power dissipation, GaN PA is very cost-effective.
Cree / WolfSpeed CGHV14800F (1200 to 1400 MHz, 800 W Devices) is the latest GAN-based PA representative. This HEMT PA has an energy efficiency, gain, and bandwidth combinations to optimize the pulse L-band radar amplifier to enable designers to find many uses in air traffic control (ATC), weather, defense and target tracking systems. With a 50 V power supply, 50% and higher typical energy conversion efficiency is provided, and 10 x 20 mm ceramic package is used with metal flange for cooling (Figure 7).
The CGHV14800F is powered by a 50 V power supply, typically provides 14 dB power gain, energy conversion efficiency> 65%. Like LNA, the evaluation circuit and reference design are critical (Figure 8).
Many specification sheets and performance curves are equally important that the power dissipation drop curve (Figure 9). The curve shows the relationship between the available power output rating and the temperature of the housing, indicating that the maximum allowable power is 115 ° C, and then linearly reduces the maximum rated value of 150 ° C.
Macom also provides GaN-based PAs, such as NPT1007 GaN transistors (Figure 10). Its DC to 1200 MHz frequency span is suitable for broadband and narrowband RF applications. The device typically operates at a single source between 14 and 28 V, which provides 18 dB of small signal gain at 900 MHz. This design is intended to withstand 10: 1 SWR (standing wave ratio) does not match, and does not generate degradation.
In addition to displaying 500, 900 and 1200 MHz, the NPT1007 supports various "load stretching" maps to ensure that the circuit and system designers of the stable product (Figure 11) provide assistance. The load tensile test is accomplished using a signal source and a signal analyzer (spectrum analyzer, power meter or vector receiver).
This test requires an impedance change of the device under test (DUT) to evaluate the performance of PA (including factors such as output power, gain, and energy efficiency), because all relevant component values may be due to temperature changes or due to their nominal Variation changes in the tolerance band.
Regardless of which PA process is used, the output impedance of the device must be fully characterized by the supplier, so that the designer can correctly match the device to the antenna, achieving the maximum power transmission and maintains SWR as much as possible. The matching circuit is mainly composed of capacitors and inductors, and can be implemented as a discrete device, or manufactured as part of a printed circuit board or even product package. Its design must also maintain the PA power level. Re-reiterate the use of tools such as Smith, it is the key to understand and carry out the necessary impedance matching.
In view of the smaller chip size and higher power level, the package is a key issue for PA. As previously mentioned, many PAs are widely refined by wide heat dissipation packaging leads and flanges, and the heat sink under the package is dissipated, as the path to the printed circuit board copper. At higher power levels (about 5 to 10 W), PA can have a copper cap, allowing the heat sink to top and may require a fan or other advanced cooling technique.
GaN PA-related rated power and small dimensions mean that hot environment modeling is critical. Of course, it is not enough to keep the PA itself in the allowable case or the junction temperature range is not enough. The heat from PA is not possible to bring problems with other parts of the circuit and system. The processing and solve the entire heat path must be considered.
Summarize
Radio-frequency systems are pushing LNA and PA performance from smartphones to VSAT terminals and phased radar systems. This allows the device manufacturer to no longer be limited to silicon, but explores GaAs and Ga to provide the desired performance.
These new process technologies provide designers with wider, smaller packages, and higher energy efficiency. However, designers need to understand the basics of LNA and PA operations to effectively apply these new technologies. "
Our other product:
