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A programmable analog radar signal design

In Electronic Infomation Category: A | on April 26,2011

Technology in the digital waveform generator, due to a direct digital synthesizer (DDS) technology has many advantages, has been in the military and TK11130CSCL datasheet and civilian fields are widely used, through a variety of waveform generator based on DDS technology, combined with the control program to arbitrary waveform can be generated.

1 overall design diagram AD9858 DDS chip

the operating frequency of up to 1 GHz, 450 MHz output signal, so choose it to generate the radar signal. In order to achieve rapid transformation and TK11130CSCL price and radar signal pulse duty cycle control, we need to control the use of faster chips, the maximum speed for C8051F340 MCU can reach 48 MHz, and TK11130CSCL suppliers and work with lines, only 20 ns to execute an instruction speed to meet demand. DDS chip to output signals, will need 2 times the output signal of the reference signal, where the selected National Semiconductors LMX2531 chip, which integrates PLL, VCO and low noise and high precision of the LDO, the shock 40MHz input signal, through the microcontroller to set its internal registers, can output a stable AD9858 1 GHz signal as a reference signal.

overall design diagram of Figure 1

2 source hardware design

2.1 Control Circuit Design

The system control chip microcontroller Silicons C805117340. It has high-speed, pipelined 8051-compatible microcontroller core (up to 48 MI s-1), accurate calibration of the 12 MHz internal oscillator and 4x clock multiplier, Universal Serial Bus (USB) function controller , 8 flexible endpoint pipes, integrated transceivers and 1 kB FIFO RAM, 64 kB of on-chip Flash memory, hardware implementation SMBus/I2C, enhanced UART, and Enhanced SPI serial interface, four general-purpose 16-bit timer device, with five capture / compare modules and watchdog timer function programmable counter / timer array (PCA) on-chip power-on reset, VDD monitor, and the Missing Clock Detector up to 40 ports I / O. It can be used on the AD9858 chip and the LMX2531 the appropriate settings.

Specific design and pin shown in Figure 2. P0.0 ~ P0.4 respectively connected LMX2531 of DATA, CLK, LE, CE. P1.2 ~ P1.7 pin access control AD9858, P2.0 ~ P3.5 DDS 8-bit data access lines and 6 address lines.

Figure 2 center control circuit

2.2 DDS signal generator circuit unit

Generated by AD8958 analog radar signal, the reference clock is 1 GHz oscillation signal provided by the LMX2531, received the AD9858s 33 feet and 34 feet. Figure 3 shows the AD9858 in the external circuit connection diagram. C8051F340 its internal use of frequency, phase register set to the required output signal.

Figure 3 DDS signal generator circuit

2.3 reference signal generation circuit

DDS chip AD958 output to make high-frequency signals must be given its high frequency precision reference clock. The LMX2531 chip can meet the demand.

LMX2531 is a low-power, high-performance frequency synthesizer, it is fully integrated PLL and VCO circuits. And the internal integration of low-noise, high precision low dropout regulator LDO, making the system has a higher noise reduction performance and stability. When used in conjunction with the high quality reference oscillator, can generate stable, low noise local oscillator signal. LMX2531 is a monolithic integrated circuit, the use of advanced BICMOS production process. LMX2531 There are several different models, each for a different frequency band. The chip uses three-wire Microwire interfaces makes programming easier way, the interface voltage as low as 1.8 V. Power supply range of 2.8 ~ 3.2 V. LMX2531 is 36 pins (6 mm 6 mm 0.8 mm) lead LLP package. PCB board size can be reduced, so use it to generate a reference clock circuit. LMX2531 external circuit shown in Figure 4.

Figure 4 LMX2531 peripheral circuits

2.4 PC control software

The circuit through the PC software and microcontroller communication, flexibility and control produce simulated radar signal carrier frequency, pulse width, repetition frequency. VC6.0 software design using PC control software, the interface shown in Figure 5. Can produce a rich variety of radar signals. For example, a single carrier frequency pulse signal, frequency agile signals, frequency hopping signals, changes in the signal repetition frequency, pulse width change signal, but also have a linear FM signal and the phase-encoded signals. In addition, you can also generate simulated radar jamming signals, such as the FM signal and random noise, hollowed out signals.

Figure 5, source control software

By setting the signal source output can be required to accurately simulate the radar signal. The following mixed signals to generate the frequency re-explained. Figure 6 (a) to set the output signal generated triple-frequency mixed signal, Figure 6 (b) for the mixed signal generated by repetition, repetition frequency signal can be seen in the step increases. In Figure 6 (c) is amplification of the carrier frequency signal, can be seen that the measured carrier frequency of 100 MHz.

Figure 6, the differential signal output pulse width

3 Conclusion

This design highlights the flexibility of the output signal, and the circuit chips are used in chip packaging, the final production of smaller circuit can output rich analog radar signals, but also demonstrated its strong capabilities. After tests showed that the signal in function of the system to meet the requirements of the performance indicators of the program were high, confirming the feasibility and forward-looking, and in phase noise, spurious suppression degree of harmonic suppression degree has a better performance.

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