1C31203G01 Based on the future chip and equipment manufacturers are bound to strengthen the construction of test labs, while using more up-to-date test equipment to simulate the actual RF network environment, and test the high stability and scalability of the products and network solutions, inexpensive and flexible expansion of the function of the R & D and verification tools are bound to have its market. In this paper, we propose to use the recently launched PXI-9820 high-speed data acquisition card of Synerchip Technology as the core to design a set of real-time Error Vector Magnitude (EVM) test system for WLAN transmitter modules, which is low-cost, elastic in function, and suitable for large-scale replication.

The 1C31203G01 controller executes the signal control procedure of the wireless NIC, and through the card bus, the wireless NIC continuously outputs the Tx signal to be measured. Since the output signals from the card are differential ended (I+, I-, Q+, Q-), but the signal acquisition card we use is a single ended input with two channels, a conversion circuit is needed to complete the process. The differential signal is converted to single-ended output, which is implemented by the Evaluation board of Analog Device Instrument (ADI). Finally, the fundamental frequency IQ signal to be analysed is inputted into the PXI-9820 and analysed by the in-house real-time I-Q signal analysis program on the PXI-3800, such as FFT and EVM. Figure 2 shows the actual baseband transmitter module test system.

1C31203G01 The physical layer (PHY) uses OFDM (Orthogonal Frequency Division Multiplexing) technology to combine a large number of signals from different frequency carriers into a single signal to complete the signal transmission. At the transmitter (Tx, Transmitter), each signal packet (frame) is transmitted before using the inverse Fast Fourier Transform (IFFT) to modulate the transmitted signal; then the phase-amplitude modulation (IQ modulation, I: in-phase, Q: quadrature) will be used to take out the phase-amplitude signals; finally, the phase-amplitude signals will be taken out by the RF (Radio Frequency, RF). Finally, a Radio Frequency (RF) circuit is used to up-convert the signal from the base band to the 5G Hz band and transmit it out. The receiver first downconverts the RF signals to the base band, then demodulates the IQ signals, and then uses the Fast Fourier Transform (FFT) to reduce each transmitted signal packet.