Analysis of the "Signal" topic in the National College Student Electronics Contest

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Analysis of the "Signal" topic in the National College Student Electronics Contest [Copy link]

1. Previous " Signal Source " Competition Topics

In the 11th National Undergraduate Electronic Design Competition, there were only five signal source questions [ 1] :

①Signal Generator (8th session , 2007 , Topic H , Vocational and Technical College Group)

②Sine signal generator (7th session , 2005 , Topic A )

③ Voltage-controlled LC oscillator ( 6th session, 2003 , Topic A )

④ Waveform Generator (5th , 2001 , Topic A )

⑤ Practical Signal Source (2nd session , 1995 )

Signal source questions have not appeared as independent questions in recent competitions, but have appeared as part of other questions.

Example 1 : Design requirements for the 2013 undergraduate group E topic “ Simple frequency characteristics tester ” :

According to the zero-IF quadrature demodulation principle, a dual-port network frequency characteristic tester is designed and manufactured, including amplitude-frequency characteristics and phase-frequency characteristics. An orthogonal sweep signal source is designed and manufactured, with a frequency range of 1MHz~40MHz , a frequency stability of ≤10-4 , and a frequency that can be set, with the minimum setting unit being 100kHz . The frequency characteristic tester has an input impedance of 50Ω and an output impedance of 50Ω . Point frequency measurement can be performed, with the absolute value of the amplitude-frequency measurement error being ≤0.5dB , and the absolute value of the phase-frequency measurement error being ≤5. Make a

The RLC series resonant circuit is used as the network under test. The DDS chip used as the signal source is specified , AD9854ASVZ (with

AD9854ASQ equivalent).

Example 2 : Design requirements for the 2011 undergraduate group E topic “ Simple digital signal transmission performance analyzer ” :

Design and make a simple digital signal transmission performance analyzer to realize digital signal transmission performance testing; at the same time, design and make three low-pass filters and a pseudo-random signal generator to simulate the transmission channel.

Design and make a digital signal generator: the digital signal V1 is an m - sequence of f1 ( x )=1+ x2 + x3 + x4 + x8 , and its clock signal is V1 -clock ; the data rate is 10~100kbps , adjustable in 10kbps steps. The output signal is TTL level.

Design and make a pseudo-random signal generator to simulate channel noise: the pseudo-random signal V 3 is f 2( x )

=1+ x + x 4 + x 5 + x 12 m- sequence ; the data rate is 10Mbps , the peak-to-peak value of the output signal is 100mV , and the clock signal V 1-clock generated by the digital signal generator is used for synchronization. The signal eye diagram of the digital signal V 2a is displayed , and the eye amplitude is tested.

Example 3 : 2013 National Undergraduate Electronic Design Competition Comprehensive Assessment Question Design Requirements:

Use the 555 chip on the comprehensive test board specified in the question and a general-purpose four-op-amp 324 chip to design and make a waveform generator. The design and production requirements are as follows:

At the same time, the four channels output, each channel outputs one of the waveforms of pulse wave, sawtooth wave, sine wave I , and sine wave II , and the load resistance of each channel output is 600 ohms. The frequency relationship of the four waveforms is 1 : 1 : 1 : 3 ( 3rd harmonic): the output frequency range of pulse wave, sawtooth wave, and sine wave I is 8kHz-10kHz , and the peak-to-peak value of the output voltage amplitude is 1V ; the output frequency range of sine wave II is 24kHz-30kHz , and the peak-to-peak value of the output voltage amplitude is 9V ; the output waveforms of pulse wave, sawtooth wave and sine wave should have no obvious distortion (when measured with an oscilloscope). The frequency error is not more than 10% ; the peak-to-peak error of the output voltage amplitude in the passband is not more than 5% . The duty cycle of the pulse wave can be adjusted. The power supply can only use a +10V single power supply, which is supplied by a regulated power supply.

Note: Do not add 555 and 324 chips, and do not use any other devices or chips except the chips on the integrated test board.

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2. Main knowledge points of previous " Signal Source " competition questions

Based on the previous " Signal Source " competition questions, the main knowledge points that students who focus on the " Signal Source " competition questions need to understand are as follows:

Use single chip microcomputer + DAC to generate various signals

Use dedicated DDS chip + single chip microcomputer to generate various signals

Use FPGA to generate various signals

DAC circuit design and production

Filter circuit design and production

Design and production of DDS interface circuit

Power amplifier circuit design and production

Power circuit design and production

Design and production of single chip microcomputer minimum system

Design and production of frequency, period and other parameter measurement circuits

Example 1 : Signal Generator ( 2007 H topic, higher vocational and technical group)

You are required to design and make a signal generator (Note: this question is based on the sine signal generator in Question A in 2005 ). Knowledge points to master:

Use dedicated DDS chips (such as AD9834 , AD9852 , etc.) and microcontrollers to generate sine, square and triangle wave signals

Use FPGA (Xilinx's DDS v5.0 DDS IP core, Altera's DDS IP core) to implement DDS functions

DAC (e.g. MAX5181/MAX5184, AD9740) circuit design and production

Design and production of variable gain amplifier circuits (such as AD603 )

Design and fabrication of power amplifier circuits (e.g. THS3001 current feedback amplifier)

Power supply circuit design and production

Design and production of single chip microcomputer minimum system

Example 2 : Sine signal generator ( 2005 A question)

It is required to design and make a sine signal generator. Knowledge points to be mastered:

Use a dedicated DDS chip (such as AD9852 , etc.) and a single-chip microcomputer to generate a sine wave signal

Use FPGA ( Xilinx 's DDS v5.0 DDS IP core, Altera 's DDS IP core) to implement DDS functions

Design and production of filter circuits (e.g. 7th order Chebyshev filter using inductors and capacitors ) Design and production of DDS interface circuits

Design and fabrication of amplifier circuits (e.g. AD8320 )

Power supply circuit design and production

Design and production of single chip microcomputer minimum system

Example 3 : Voltage-controlled LC oscillator ( 2003 Problem A )

You are required to design and make a voltage-controlled LC oscillator. Knowledge points to master:

Design and production of voltage-controlled oscillator circuits (e.g. voltage-controlled oscillator chip MC1648 + varactor diode MV209 )

Design and production of digital phase-locked loop frequency synthesizer circuit (for example, PLL MC145152 + pre-divider MC12022 + VCO MC1648 + loop filter LM358 and RC ) Design and production of FPGA minimum system

Peak - to- peak detection circuit design and production

Frequency measurement circuit design and production

Design and production of high frequency power amplifier circuits

Filter circuit design and production

Power supply circuit design and production

Design and production of single chip microcomputer minimum system

LED or LCD display circuit design and production example

4. Waveform Generator ( 2001 Question A )

It is required to design and make a waveform generator. Knowledge points to be mastered:

Use direct digital frequency synthesis ( DDFS ) technology to generate waveform

Crystal oscillator and phase-locked loop circuit design and production

Special memory dual-port RAM circuit design and production

Waveform generation circuit design and production

Filter circuit design and production

Design and production of stable output circuit

Single chip microcomputer minimum system design and production example

5. Practical signal source ( 1995 )

It is required to design and make a practical signal source. Knowledge points to be mastered:

Use MCU + DAC to generate sine wave signal

Comparator circuit design and production

Filter circuit design and production

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3. Some suggestions for training on “ Signal Source ” competition questions

Although signal source topics have not appeared in recent competitions, they may appear as signal sources in works in radio, instrumentation, data acquisition and processing, etc. Therefore, they are still an important training content that cannot be ignored in competition training.

Each team must master several basic knowledge and techniques related to signal generation, circuit design and production (for example: DDS , FPGA , oscillator circuit composed of operational amplifiers, power amplifier circuits, filter circuits, impedance matching, etc.).

These contents serve as basic training for the competition and can be carried out before grouping (dividing the competition topics).

According to the design requirements of the comprehensive assessment questions of the National College Student Electronic Design Competition in 2011 and 2013 , teams that have the opportunity to win the national first prize need to strengthen training in this area after completing the 4- day and 3- night competition.

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