Just like life itself, we often tell ourselves that if we push a little harder today, tomorrow will surely be easier. The same holds true for RF design – we always hope that the next project will have slightly looser requirements, be a little simpler to design, or at least match the difficulty of the current one. But reality rarely cooperates. The pitfalls we avoid today are often deeper tomorrow, and the challenges we overcome today are often the simplest we will ever face. Of course, this is precisely where the value of us engineers lies...
Today, virtually every electronic product strives to integrate as many functions as possible. This is especially true for mobile phones – from the original telephone, voice, and text messaging functions, to today's data, images, video, music, wireless connectivity, navigation, gaming, and even many features we have never used – they have become all‑in‑one compact devices for work, entertainment, and learning. The integration of all these applications has undoubtedly increased the complexity of RF design, making the design task exceptionally difficult.
The best way to solve this design challenge is to achieve an organic combination of RF analogue design with digital sections, hardware with software, and chips with PCBs. RF analogue design must merge with digital system design, rather than being a rigid assembly of disparate parts. The combination of hardware and software design places ever‑higher demands on engineers. Naturally, this also drives engineers to design and develop higher‑integration, more functional SoCs (Systems on Chip), minimising the number of discrete components on the PCB.
In many companies, the era of "one person, one role" is gradually coming to an end. We can no longer immerse ourselves solely in our own domain, completing only our own design tasks while paying little or no attention to what others are doing. The demand for cross‑disciplinary talent is growing in RF design. A good RF engineer must be able to break through the boundaries of their own knowledge and skills, integrating digital design, signal processing, and SoC technologies to create better products.
During my university days, I picked up a Nokia 3230 at a campus second‑hand market. In that era, Nokia was the undisputed king of mobile phones – sturdy, robust, and feature‑packed. But compared with today's smartphones, it was like a brick – in size, weight, and functionality. Yet today's incredibly powerful phones can slip easily into a pocket – lightweight and fast. Without the advent of highly integrated ICs, this level of design complexity would be unimaginable. The successful development of highly integrated RF analogue SoCs came later than that of digital baseband ICs. In fact, the emergence of SoCs has not only made it possible to create smaller wireless products with more complex features, but has also made direct‑conversion receiver architectures feasible. The advancement of RF analogue IC technology has made RF SoCs a reality – where a single chip is an RF transceiver.
The RF system we design is actually just a front‑end subsystem of the entire wireless digital transceiver. The performance of the digital baseband and the RF analogue system interact with and complement each other.
For a given sensitivity, the performance of the baseband demodulator and processor gain determines the noise figure of the RF transceiver. Similarly, in the RF receiver chain, to achieve a certain bit error rate (BER), the group‑delay distortion after channel filtering affects the minimum required signal‑to‑noise‑plus‑interference ratio (SNIR). Because received signal strength is now measured in the digital domain – rather than using analogue power detectors as in the past – the automatic gain control (AGC) of the RF receiver is closed‑loop within the digital baseband system. Likewise, on the transmit side, the transmit power is controlled by the digital baseband. By adjusting the level ratio of the digital baseband signals in the I/Q channels, DC offset and I/Q imbalance can be compensated.
In the receive chain, the interface between RF and the digital baseband is the ADC; on the transmit side, the interface is the DAC. The dynamic range or resolution of the ADC and DAC affects the gain control range and the signal quality at both the RF receiver and transmitter. Therefore, joint RF‑digital design is an inevitable trend, and RF engineers are expected to have knowledge of digital baseband and modern communication theory.
In addition, RF software is becoming increasingly important. RF systems require more and more software control and support. Digital signal processing and related software applications are also growing in importance in RF system design – for example, automatic gain control (AGC), RF band selection, and channel selection all require embedded DSP execution. Especially in future software‑defined radio (SDR) systems, embedded DSP capability may become a mandatory skill for RF engineers.
Will RF antennas and filtering modules one day become programmable, just like digital basebands?
Learning never ends – and this is especially true for RF engineers. Only by continuously keeping up‑to‑date with new technologies and knowledge can we avoid being left behind in this wireless revolution.