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Tektronix AWG 2021 Brochure

Signals and measurements for wireless communications testing
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Signals and Measurements for
Wireless Communications Testing

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Summary of Contents for Tektronix AWG 2021

  • Page 1 Signals and Measurements for Wireless Communications Testing...

  • Page 2: Table Of Contents

    13 Filtering Out Unwanted Sidebands ..... . . 25 14 Direct Sequence Spread Spectrum For More Information on Tektronix Instrumentation ....29 AWG 2000 Series Arbitrary Waveform Generators TDS 744A Digitizing Oscilloscope .

  • Page 3: Introduction

    The TDS 744A is an ideal complement to the AWG 2021 and is unique in its ability to capture signal minutiae. Certain test setups described in this book may...

  • Page 5: Analog Carriers And Modulation

    Analog Carriers and Modulation Basic Sine Wave Amplitude Modulation (AM) The best introduction to the AWG is to parallel the procedure of generating a carrier with a conventional signal generator. With a signal generator, one simply enters the carrier frequency and the output ampli- tude, such as 1000 kHz at 0 dBm.
  • Page 6 A record length must be selected that has an adequate number of points to reconstruct the desired waveform. The waveform period is 1 ms and there are 1000 carrier cycles in this period. A record length of 20,000 points would allocate 20 points per cycle, which adequately over- samples the ideal waveform.

  • Page 7: Am With Adjacent Carriers

    AM with Adjacent Carriers A simple addition to the AM signal demonstrates the flexibility of equation-based waveform descriptions. A common task in evaluating receiver performance is to evaluate the effect of adja- cent carriers. For the basic AM signal, one can easily add modu- lated carriers 10 kHz above and below the original signal (Figure 4).
  • Page 8 1000 1005 1010 1015 Frequency (kHz 1020 Figure 6. Spectrum analyzer plot of the 3 carriers. There are 3 kHz AM on the adjacent carriers and 1 kHz AM on the original carrier. Note the low level of close-in spurious components.

  • Page 9: Multi-Tone Testing

    Multi-Tone Testing The logical extension of adjacent carrier testing is multi-tone test- ing. In addition to simulating multiple carriers in a multi- channel system, multi-tones can quickly test filter response when a scalar or network analyzer is not available, or they can iden- tify intermodulation products resulting from saturation or non- linearities in supposedly linear...
  • Page 10 The 11 tone equation was then modified so that the last 5 tones (71 through 75 MHz) are inverted. The two different multi-tone results are shown in Figure 9. The scope shows that the rms levels of the two signals are identical, but the peak-to- peak values are different.

  • Page 11: Frequency Modulation

    Frequency Modulation Frequency modulation introduces control of the phase argument, , in the basic carrier equation: A sin ( c t + FM is implemented by varying in direct proportion to the integral of the modulating signal. Thus, for a modulating signal m(t), the FM signal can be written: A sin ( c t + k m(x) dx )

  • Page 12: Fm With Dual-Tone Modulation

    FM with Dual-Tone Modulation While basic single-tone FM is a built-in function of virtually all conventional signal generators, dual-tone FM modulation clearly contrasts the flexibility of the AWG approach. Dual-tone modulation tests can be used to measure intermodulation prod- ucts in a noise reduction compandor (compressor- expander) in FM receivers such as cordless phones.
  • Page 13 Figure 13 shows the demodu- two-tone signal and its spectrum lated output from an FM as calculated by the TDS 744A receiver with the expander FFT function. The lower two disabled and enabled. The top traces show the same signals two traces show the unexpanded with the expander enabled.

  • Page 14: Fm Stereo

    FM Stereo A final example of conventional analog modulation combines most of the above techniques to simulate the stereo modulation used in broadcast FM. The modulating signal consists of three components, 1) the composite audio which is the sum of the left and right (L+R) channels, 2) the stereo pilot signal which is a 19 kHz tone, and 3) the difference (L-R) signal...
  • Page 15 The resulting 455 kHz signal is traces are the right channel mixed up to the broadcast band (1000 Hz) signal and spectrum. and inserted into a stereo The lower two traces are from receiver. The stereo indicator is the left channel (800 Hz). The turned on, and the resulting left stereo encoding was successful and right output signals are...

  • Page 16: Adding Noise To A Carrier Signal - Awg Noise Characteristics

    Adding Noise to a Carrier Signal — AWG Noise Characteristics Although the removal of noise is a common design goal, a noise source can be an extremely useful test stimulus or signal impairment. The AWG 2041 provides a built-in noise func- tion, but its characteristics are quite different than traditional sources such as noise diodes.
  • Page 17 the AWG’s 10 MHz low-pass account for the clock rate depen- dent roll-off. filter (middle trace). The TDS 744A FFT spectra for the Maximizing “Randomness” two signals are overlaid below The second property to consider the time domain waveforms. The when using the AWG noise salient characteristic of the waveform is to observe that the...
  • Page 18 The AWG’s graphical waveform editor provides a variety of mathematical operators for exist- ing waveforms. Waveforms can be combined with other waveforms, or a waveform can be squared, scaled, differenti- ated, integrated, etc. Combining the Noise with the Carrier The signal and noise waveforms are summed using the AWG’s 10670 10680...

  • Page 19: Digital Modulation

    Digital Modulation Digital Phase Modulation — PSK The modulating signals in the foregoing examples have been sinusoidal or continuous wave- forms. A simple step to digital modulation is made with a slight variation to sinusoidal modula- tion. Figure 21 shows one cycle of a sinewave that has been quantized into steps between –0.5 and +0.5.
  • Page 20 Figure 22. The equation defining the quantized 1 MHz modulating pattern and its subsequent insertion into the phase argument of the 50 MHz carrier. The modulating pattern shown in Figure 21 is the result of the rounding definition. The record length of 1024 points Figure 23 shows the resulting and a waveform period of 1 µs AWG output.

  • Page 21: Baseband Digital Patterns

    Baseband Digital Patterns Before continuing with exam- ples of digital modulation, it is important to establish a method of creating arbitrary test data patterns. Figure 24 shows direct entry of a 28-bit binary pattern. In this case, the 0 or 1 value of each data bit is repeated for 1000 points in the record, which requires a record length of...

  • Page 22: Digital Am - Ook And Bpsk

    Digital AM — OOK and BPSK The simplest example of digital modulation is to turn the carrier on or off, depending on the state of the modulation data. On-off keying (OOK) can be directly implemented by multiplying a carrier by the 1 or 0 value of the data pattern.

  • Page 23: Digital Fm - Fsk

    Digital FM — FSK The modulating data alters the carrier frequency in frequency-shift keying (FSK). A digital modulation index of 0.5 is used in this example; that is, the frequency shift will be 40 kbaud data rate or 20 kHz. If the carrier remains centered at 10.7 MHz, this results in the two data frequencies of 10.710 MHz...
  • Page 24 As previously mentioned, the AWG’s two binary marker output signals can be modulated with a data pattern. Figure 30 shows how this can be used as a tool for testing or troubleshooting digital receivers. One marker output is programmed to generate a trigger pulse at the beginning of each 700 µs record (top trace).

  • Page 25: Quadrature Modulation

    Quadrature Modulation Multi-level data modulation splits the amplitude, frequency, or phase of the carrier into more than two discrete states. 8-PSK previously demonstrated direct control of the phase equation A cos( c t + ); A was constant. The eight symbols were equally spaced points around the polar axes.
  • Page 26 (upper) and an amplitude modulated sine carrier. There are 16 symbols, so this is 16-QAM. Oscilloscope (DSO) Figure 33. This block diagram shows the setup for quadrature modulation. For more information about suitable RF sources, contact your local Tektronix representative.

  • Page 27: Filtering Out Unwanted Sidebands

    Filtering Out Unwanted Sidebands One effect of the edge transitions in digital modulation patterns is a wider than desired occupied spectrum of the transmitted signal. The solution is to filter the baseband digital signal before it modulates the carrier. The two most common filter types for this application are Gaussian and Nyquist filters.
  • Page 28 The convolution result is 30,000 points long. Note that the impulse response is 2000 points long, which is longer than the 1000 points per data bit. This means that each data bit affects more than the 1000 points that it immediately occupies.
  • Page 29 Figure 36 compares the original modulating (BPSK) the and filtered data patterns. The 10.7 MHz carrier, as in Figure 27. upper two traces are the unfil- Figure 38 shows the difference tered data pattern and its spec- in their spectra. trum.

  • Page 30: Direct Sequence Spread Spectrum

    Direct Sequence Spread Spectrum The final example of digital modulation spreads the energy in a BPSK signal by amplitude modulating the carrier with a spreading pattern. In the same way that the baseband data pattern spreads the energy of an unmodulated carrier, a spread- ing pattern further spreads the energy of a modulated carrier.

  • Page 31: For More Information On Tektronix Instrumentation

    AWG 2005 data sheet ......11372 AWG 2021 data sheet ......11561 AWG 2041 data sheet .

  • Page 32: Awg 2000 Series Arbitrary Waveform Generators

    Where the utmost signal purity For computer-controlled produc- is required, the AFG 2020 tion test applications demanding Arbitrary Function Generator high throughput, the AWG 2021 offers direct digital synthesized is available in VXI format as the waveforms with exceptionally VX4792. This uncompromised...

  • Page 33: Tds 744A Digitizing Oscilloscope

    TDS 744A Digitizing Oscilloscope The TDS 744A represents the next generation of digitizing scope performance. This versa- tile general-purpose instrument introduces Tek’s new InstaVu acquisition feature and sets a benchmark in waveform capture rate for DSOs. The TDS 744A can display more than 400,000 Bandwidth Input Channels Sample Rate per Channel...
  • Page 36 Brazil and South America 55 (11) 3741 8360; Canada 1 (800) 661-5625; Denmark 45 (44) 850700; Finland 358 (9) 4783 400; France & North Africa 33 (1) 69 86 81 08; Germany 49 (221) 94 77-400; Hong Kong ( 852) 2585-6688; India 91 (80) 2275577; Italy 39 (2) 250861; Japan (Sony/Tektronix Corporation) 81 (3) 3448-4611; Mexico, Central America, & Caribbean 52 (5) 666-6333;...

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Awg 2000 series

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