Millimeter wave signals provide wider bandwidth and higher data rates than low frequency signals. Take a look at the overall signal chain between the antenna and the digital baseband.
New 5G radio (5G NR) adds millimeter wave frequencies to cellular devices and networks. Along with this comes an RF-to-baseband signal chain and components that are not required for frequencies below 6 GHz. While millimeter wave frequencies technically span the range from 30 to 300 GHz, for 5G purposes they span from 24 to 90 GHz, but typically peak at around 53 GHz. Millimeter wave applications were initially expected to provide faster data speeds on smartphones in cities, but have since moved to high-density use cases such as stadiums. It is also used for fixed wireless access (FWA) internet services and private networks.
Key benefits of 5G mmWave The high throughput of 5G mmWave allows for large data transfers (10 Gbps) with up to 2 GHz channel bandwidth (no carrier aggregation). This feature is best suited for networks with large data transfer needs. 5G NR also enables low latency due to higher data transfer rates between the 5G radio access network and the network core. LTE networks have a latency of 100 milliseconds, while 5G networks have a latency of just 1 millisecond.
What’s in the mmWave signal chain? The radio frequency interface (RFFE) is generally defined as everything between the antenna and the baseband digital system. RFFE is often referred to as the analog-to-digital portion of a receiver or transmitter. Figure 1 shows an architecture called direct conversion (zero IF), in which the data converter operates directly on the RF signal.
Figure 1. This 5G mmWave input signal chain architecture uses direct RF sampling; No inverter required (Image: Brief description).
The millimeter wave signal chain consists of an RF ADC, RF DAC, a low pass filter, a power amplifier (PA), digital down and up converters, a RF filter, a low noise amplifier (LNA), and a digital clock generator (CLK). A phase-locked loop/voltage controlled oscillator (PLL/VCO) provides the local oscillator (LO) for the up and down converters. Switches (shown in Figure 2) connect the antenna to the signal receiving or transmitting circuit. Not shown is a beamforming IC (BFIC), also known as a phased array crystal or beamformer. The BFIC receives the signal from the upconverter and splits it into multiple channels. It also has independent phase and gain controls on each channel for beam control.
When operating in receive mode, each channel will also have independent phase and gain controls. When the downconverter is turned on, it receives the signal and transmits it through the ADC. On the front panel there is a built-in power amplifier, LNA and finally a switch. RFFE enables PA or LNA depending on whether it is in transmit mode or receive mode.
Transceiver Figure 2 shows an example of an RF transceiver using an IF class between baseband and the 24.25-29.5 GHz millimeter wave band. This architecture uses 3.5 GHz as the fixed IF.
The deployment of 5G wireless infrastructure will greatly benefit service providers and consumers. The main markets served are cellular broadband modules and 5G communication modules to enable the Industrial Internet of Things (IIOT). This article focuses on the millimeter wave aspect of 5G. In future articles, we will continue to discuss this topic and focus in more detail on the various elements of the 5G mmWave signal chain.
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Post time: Sep-12-2024