Overview

Satellite navigation technology has become a widely adopted positioning technology in human activities and rapidly developed into an emerging industry—the satellite navigation and positioning industry. The United States and Russia have successfully built global satellite navigation systems, GPS and GLONASS, respectively, and the European Union is currently constructing the GALILEO system. In 2000, China launched two satellites for its Beidou Navigation Satellite System (BDS), marking a breakthrough in China’s satellite navigation technology. This made China the third country in the world to have an independent satellite navigation system.

Unlike GPS, the Beidou Satellite Navigation System utilizes an active two-way ranging navigation system. The Beidou system consists of two geostationary satellites, a central control system, a calibration system, and various user devices. The central control system sends inquiry signals to the two satellites, which are then retransmitted to users in the service area. Users respond to one satellite’s inquiry signal and send a response to both satellites, which is then relayed back to the central control system. The control system receives and decodes the user’s signals, processing them accordingly based on the requested service.

Although the Beidou generation satellite system offers communication capabilities, its active positioning method limits factors such as user capacity, positioning accuracy, stealth, and frequency of positioning. With improvements in the Beidou generation satellite positioning baseband processing algorithm, passive positioning with three satellites has now been achieved. In 2005, China successfully developed the first Beidou I satellite passive positioning receiver, which solved the issue of real-time fast positioning independently. It provides all-weather, high-precision, real-time navigation and positioning services for China and surrounding regions. The ongoing maturity of Beidou generation passive positioning greatly expands the potential applications of Beidou generation terminal products.

A key application of Beidou generation terminal products is single-receiver time synchronization, which is essential for many industries, such as communication base stations and power sectors. Currently, these industries rely on GPS for time synchronization, but it is becoming increasingly clear that adopting Beidou time synchronization will be the trend, with a very large demand.

The RNC2410 RF Chip: A Key Innovation for Beidou Generation

To meet the demand in the Beidou generation single-receiver market, a Chinese company developed the Beidou generation RF single-receiver chip RNC2410. The RNC2410 offers superior performance, low power consumption, high stability, and a compact size. It requires only a few external components to achieve the RF reception function of the Beidou generation, significantly reducing the product’s volume and system cost.

Key Features of the RNC2410

The RNC2410 is a radio frequency (RF) receiver chip designed for the Beidou Generation satellite navigation system. The chip integrates all receiver channel modules and frequency synthesizers. The receiver channel provides both analog signal output and ADC-quantized signal output, along with sampling clock output. With a few external components, the chip can achieve the reception function required for Beidou user devices. It uses the standard SPI interface protocol for communication.

The chip adopts a two-stage frequency conversion structure. The receiver first down-converts the RF signal to the first intermediate frequency (IF) through the RF front-end circuit, and then further down-converts the first IF to the final IF output through a second mixer. With proper frequency planning, this greatly improves the receiver’s image suppression and channel selectivity. To enhance the chip’s integration and reduce the number of external components, the chip integrates a frequency synthesizer and corresponding voltage-controlled oscillators (VCOs), as well as a phase-locked loop (PLL) used to generate the ADC sampling clock. This PLL also provides the reference clock for the baseband section.

A variable gain amplifier with 1dB step control is used in the IF stage, which ensures that the output signal level remains at a peak-to-peak differential voltage of 1V through an automatic gain control (AGC) loop. The RNC2410 can provide both analog IF signals and 2-bit quantized signals.

Applications of the RNC2410

Thanks to its high integration, the RNC2410 chip simplifies system design by requiring only minimal peripheral circuitry for the reception function. Figure 1 shows the system schematic of a Beidou generation receiving terminal using the RNC2410.

In the schematic, the BDI LNA (Low Noise Amplifier) for Beidou I provides a gain greater than 42dB with a noise figure below 1.3dB. The ADC can be sourced from ADI’s AD9283 or similar products. The BDI Baseband can be implemented using a dedicated chip or FPGA.

Since the RF input of the RNC2410 is differential, and the LNA’s output impedance is single-ended (50 ohms), input matching circuits are necessary. A single-ended 50-ohm to differential 100-ohm balun is used along with a differential T-network for proper matching between the balun and chip.

To improve image suppression and channel selectivity, a high-selectivity SAW filter is used at the first IF, and matched accordingly. The RNC2410 provides two interfaces to the baseband section: one offers analog IF output, which is sampled by an external ADC to produce a quantized signal for the baseband, while the other provides quantized IF output with 2-bit resolution, directly sent to the baseband.

The test results of a Beidou I terminal using the RNC2410 show a reception sensitivity higher than -157.6dBm.

Conclusion

The RNC2410 is an independently developed RF chip for the Beidou satellite navigation system. It offers significant reductions in size and cost compared to traditional products. The module’s performance fully meets the requirements of the overall system and is currently undergoing trial use. Large-scale production is expected soon, which will drive the rapid development of China’s Beidou satellite navigation industry.