Zhejiang Microwave and Millimeter Wave RF Industry AllianceThe CX9261 developed by the subsidiary Hangzhou Chengxin Technology Co., Ltd. is a broadband, high-performance, multi-channel RF transceiver. It is designed based on the concept of software radio and integrates RF, ADC/DAC and digital required by the RF transceiver. Up-conversion and other circuits greatly reduce the complexity of RF link design, and the system has a high degree of integration. The RF transceiver has been widely used in wireless communication systems such as smart terminals, data links, and femtocell/picocell/microcell base stations.

With the continuous deepening of communication application reform with information technology as the core, various types of information application terminals have gradually increased, and they have played an active role in daily life, team activities, earthquake relief and other special operations. The broadband multi-mode RF transceiver chip CX9261 independently developed by Hangzhou Chengxin Technology Co., Ltd. can provide effective hardware support for multi-mode intelligent terminals. Application scenarios, realize the concurrent work of multiple communication modes such as broadband, narrowband, public network, private network, etc., which can greatly simplify the system design of multi-mode communication terminals.

Chip overview

CX9261 RF transceiver integrates low noise amplifier, up/down mixer, multimode filter, automatic gain control, DC offset cancellation, power intensity detection, ADC/DAC, driver amplifier, power management, fractional frequency synthesis , logic control, decimation/interpolation filtering, digital down-conversion and automatic calibration and other functions, with universal design, broadband coverage, wide and narrowband signal compatibility, low power consumption and other characteristics.
The operating frequency range of channel 1 and channel 2 of the device is 70MHz~2.7GHz, and the operating frequency range of channel 3 is 1.2GHz~1.8GHz, and the on-chip tunable bandwidth is 20kHz to 60MHz.
The device’s receive channel uses a direct-conversion architecture consisting of a low-noise amplifier, a mixer, a programmable gain amplifier, a variable-bandwidth filter, and a high-speed, high-precision 16-bit ADC. The receiving channel of the device has the calibration function, the noise figure is small, and the image rejection performance is high, which is beneficial to improve the RF performance of the receiving channel. The 16-bit ADC has a large dynamic range.
The device’s transmit channel uses a direct-conversion architecture consisting of a mixer, programmable gain amplifier, variable bandwidth filter, and a high-speed, high-precision 16-bit DAC. The transmit channel of the device has both local oscillator leakage calibration and IQ quadrature calibration, which can well suppress local oscillator leakage and image interference, with high clutter suppression and superior RF performance.
Both the local oscillator and the clock of the device use a fractional PLL, which can better suit various application scenarios. At the same time, the device also provides an external local oscillator input interface, which effectively reduces the phase deviation of multi-device applications.
The power supply of the device is 2.5V and 1.3V, and the power consumption is less than 1W under the condition of full power operation in 2.7GHz frequency, single-receiver-single-transmit FDD mode. The device is a plastic packaged BGA 289pin, 15mm×15mm. The device looks like this:

Figure 1 Physical map of CX9261 chip

Excellent device characteristics

Compared with other SDR chips, the main differences between CX9261 chip are: different number of transceiver channels, different on-chip local oscillators, different on-chip ADC/DAC bit widths, and support for fast frequency hopping. The internal functional block diagram of the chip is shown in Figure 2. Show.

Figure 2 Functional block diagram of CX9261 RF transceiver


·Channel Quantity Characteristics

From the functional block diagram of the CX9261 chip, it can be seen that it has three receiving channels and two transmitting channels. The operating frequency range of channel 1 and channel 2 is 70MHz to 2.7GHz, and the operating frequency range of channel 3 is 1.2GHz to 1.8GHz. , the on-chip tunable bandwidth is 20kHz to 60MHz. The chip channel supports external local oscillator input, and the working mode supports TDD and FDD forms.

·On-chip local oscillator characteristics

The chip has 3 independent receiving local oscillator RXPLL, 2 independent transmitting local oscillator TXPLL, and 3 independent baseband local oscillator BBPLL, all local oscillators can be configured independently. The above design enables independent settings for the operating frequency, bandwidth, sampling rate and other functions of the five RF transceiver channels on the CX9261 chip, providing effective hardware support for the design of multi-mode communication systems.

·On-Chip ADC/DAC Features

The internal ADC/DAC core of the CX9261 chip is designed with a 16-bit bit width, which is 4 bits more than the design of other zero-IF architecture SDR chips with a 12-bit ADC/DAC design. The noise floor of the CX9261 receiving channel is higher than that of the 12-bit SDR chip at a gain of 25dB. It is 12dB lower, which means that when large and small signals coexist, the ability of the CX9261 chip to detect small signals is about 12dB lower than that of the SDR chip designed by 12-bit ADC, and it has a larger dynamic range and anti-interference ability.

·Fast frequency hopping function

Through the optimization of the on-chip PLL loop of CX9261, the chip has the ability of fast frequency hopping, and the frequency stabilization time is less than 10μs.

Figure 3 CX9261 frequency hopping frequency stabilization time

Multimode Communication System Architecture

The block diagram of CX9261 for multi-mode communication system is as follows:

Figure 4 CX9261 multi-mode communication system application block diagram


·Channel 1:

It is implemented through CX9261 transceiver channel 1, the frequency range supports 70~2700MHz, and the tunable bandwidth is 20kHz to 60MHz. At the same time, the transceiver channel 1 of CX9261 supports Tiantong interface and has Tiantong communication capability.

·Channel 2:

It is realized through CX9261 transceiver channel 2, the frequency range supports 70~2700MHz, the tunable bandwidth is 20kHz to 60MHz, and the application of ultra-short wave radio is supported by the front-end frequency conversion circuit.

·Channel 3:

Through the CX9261 transceiver channel 3, the Beidou frequency can be received.

The above system application scheme makes full use of the independence of the CX9261 chip for three receiving and two transmitting channels, and realizes software self-loading and concurrent communication of five communication standards, including Tiantong, LTE, ad hoc network, ultra-short wave radio, and Beidou, as shown in Table 1.

Table 1 Concurrent combination of multi-mode communication system based on CX9261

CX9261 performance test

The CX9261 RF transceiver channel has excellent channel indicators, and its typical EVM test indicators are as follows:

Figure 5 CX9261 transmit channel 64QAM EVM test indicators

Editor: Huang Fei

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