The design engineers such as next-year aerospace and other communication systems are being advanced to the development of advanced technology, highly configurable systems, need to integrate various functions and needs, integrating the functionality of the independent system. Obviously, the advantage of this is to reduce the number of subsystems that need to be supported by the task platform, reduce overall size, weight, and power consumption (SWAP), but the challenge can be described as tapped because it is necessary to further support cognitive and real-time configuration. However, a new generation of high performance, broadband devices provide potential solutions for this challenge, not only support high performance levels of each system, but also work scope and very wide enough to address multi-functional challenges.
Many ultimate goals of such future systems are architectures that are fully determined by software, in order to be able to dynamically change, update on site or in factory configuration, implementation, without or only very small hardware changes. The challenge is that the system may need to support a variety of working modes, which requires the underlying single hardware to meet the technical specifications of all possible working modes.
An example of such systems is the radar and communication platform. In addition to multi-mode radars, the radar system also wants to support electronic support measures (ESM); communication systems are in addition to multi-waveform communication, they also want to implement signal intelligence (SIGINT).
In both cases, the system wants to integrate broadband and narrowband functions, and these functions are usually large in linearity, dynamic range, and other requirements. If the technical specifications have no rooms, in order to achieve the primary goal, the designer may have to make a step on the power consumption or size. For example, consider an X-band radar system and a broadband electronic system (ELINT). The operating frequency range of the radar system is typically relatively narrow, and typical is 8 GHz to 12 GHz band hundreds of MHz. In contrast, the operating frequency range of the ELINT system is usually 2 GHz to 18 GHz, cover all S, C and X bands. If it is assumed that the size of these two implementations must be the same, it may be necessary to make concessions to support the ELINT system's wider frequency range and override. For this example, the bandwidth can usually be exchanged with the linearity or power consumption of the signal chain.
If the same concept is applied to the device level, the same problem is observed. For broadband systems, at least one aspect of the device is affected, such as linearity, noise performance or power consumption. Table 1 below shows a typical performance of the integrated voltage controlled oscillator (VCO) and narrow-band locking rings (PLLs). It can be seen that narrowband devices have better typical phase noise, quality factor, and power consumption, but obviously this is obtained at the expense of flexibility.
Table 1. Performance comparison of typical broadband and narrowband PLL integrated VCO
Figure 1. Possible broadband re-configurable signal chain
Although in practical applications, the above architecture may require additional filtering and gain grades to achieve specific specifications, but the flexibility of the underlying device supports a very wide surveillance system architecture. In addition, the configurable digital signal processing function supports the signal chain to perform more narrowband functions when needed. What is even better is that the system can also change the mode of operation in real time, which is expected to support more features along with other digital signal processing circuits downstream.
The first two - low noise amplifiers (LNAs) and mixer systems of the signal chains shown in the figures are implemented in GaAs technology. Although the broadband SiGe mixer has made progress, the front end device is preferably used to use the GaAs and GaN devices. In both cases, both HMC 1049 and HMC 1048 provide a very wide range of performance and excellent IP3, support narrowband and broadband operations. These devices description, process progress allows individual devices to meet a variety of specifications, without having to attach digital features. The benefits of digital features embedded in RF devices can be seen in other components of the signal chain.
The new PLL ADF5355 integrates VCO, supports RF outputs of 54 MHz to 13.6 GHz, and provides a wide range of synthesizer frequencies for use. This device is based on the SiGe process, using four independently integrated VCO kernels to support rich and diverse operations. Each core uses 256 overlapping bands, so that the device can cover a wide range of frequency range without high VCO sensitivity, phase noise and spurious performance are not affected. The internal integrated digital calibration logic inside the device automatically selects the correct VCO and frequency band. The device allows the signal chain to support RF scan of 54 MHz to 13.6 GHz, and can also support fixed frequencies. At the same time, the signal chain also maintains the high performance level required for more narrowband system operations, and typical phase noise at 1 MHz offset is -138 dBc / Hz.
The ADA4961 ADC driver provides broadband performance and excellent linearity. With SPI and embedded digital control, it achieves 90 DBC IMD3 performance at 500 MHz, and 1.5 GHz is -87 dBC. Devices integrate digital control, support gain control and fast start options, so that the device can be configured as needed, optimally perform system performance. Quick start can also improve the flexibility of the system because it can quickly reduce the gain when the FA pin is driven (usually by an over-range detection output of the ADC), so that the ADC does not enter the saturation state.
The last device in the signal chain is AD9680, which is one of the latest high-speed converters. This device supports the sampling rate of up to 1 GSPS based on the 14-bit resolution based on the 65 NM CMOS process. When using a higher sampling rate and the bandwidth of the GSPS converter, the AD9680 has the ability to undertake the intermediate frequency signal at frequencies of more than 1 GHz. This is consistent with the continuation of the system's digital conversion point and improving system flexibility. The device not only provides industry-leading SFDR and SNR performance, but also integrates digital downconverting (DDC) signal processing, and output bandwidth can be customized.
The AD9680 ADC has digital signal processing configuration capabilities, which supports broadband monitoring, and supports narrowband. When disabled and bypass DDC, it supports instantaneous monitoring bandwidth of 500 MHz or more. When using DDC, the digital CNC oscillator (NCO) can be set to mix the narrowband intermediate frequency signal number to the baseband, and then reduce the data rate by the configurable extraction filter; when the device operates at the maximum ADC sampling rate, the output data band is wide. Reduce to 60 MHz. Digital signal processing not only improves the system SNR of lower bandwidth, but also provides the flexibility required to configure broadband and narrowband signal chains.
Although this example is concerned about the receiver path, similar devices and integration are also suitable for transmitters. The new DAC integration highly configurable interpolation filter and digital upper frequency conversion function can be used with the wideband radio and microwave devices described above.
The example shows how a new generation of broadband devices integrate more and more digital signal processing and functions, and how this makes the future system dynamic configuration capabilities, so that the multi-mode work is supported at an unprecedented performance level. This is contradictory with the narrowband and broadband operations that cannot coexist. It should be noted that the above simple analysis does not involve certain filtering problems or power analysis. These factors may seriously affect the actual design selection and signal chain architecture. However, with the increase of higher performance broadband devices, as well as the enhancement of signal processing, the future is highly configurable, confirmed, and the system defined by the software looks broad.
Finally, an example is given to better clarify the integrated radio frequency IC device of the AD9361, which is almost extremely extreme, further proves that the boundaries between numbers and simulation functions are getting more and more blurred. The AD9361 uses direct variable frequency architecture, integrated digital filtering and calibration, highly flexible, supporting radio frequency input frequency of 70 MHz to 6 GHz and bandwidth up to 56 MHz.
The configuration capabilities of the AD9361 support wide application, including radar, communication, and data links. Using digital calibration and processing, the device can overcome many typical issues of direct frequency conversion systems and provide unprecedented integration and configuration capabilities to further support cognitive and multi-function systems.
Previously, such high integration and performance were unimaginable. In addition, many system designers have to avoid direct frequency conversion architectures due to limitations such as mirror suppression such as frequency and temperature. The higher coupling of numbers and simulation functions, as well as integrated advanced calibration and processing functions in the current devices, providing solutions, while improving flexibility without significantly affecting performance and power consumption. Although better performance can be obtained using a narrowband dedicated signal chain composed of discrete devices, the gap is already shrinking.
The ultimate goal of the software definition system is that a radio frequency and microwave signal chain is suitable for all applications, and ideal is a single device such as transceivers to support multi-function and cognitive applications. In fact, all systems may have a distance from this goal, but the latest development and progress enables more and more new semiconductor devices integrated, and we are getting closer to the goal. In addition to improving traditional RF performance, digital signal processing can also alleviate and overcome certain multi-mode challenges. It may not be more than a long time, a single solution using a single device or a cascaded broadband device to meet all application requirements, the software definition system ultimately dreams come true.
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