Introduction to the Rigol DG1022 Waveform Generator This document serves as a supplement to the lab videos “Introduction to the Signal Generator” and “Oscilloscope & Generating AM Modulated Waves on the Signal Generator”. These videos can be found on the iPads in the sophomore labs or online at: http://vimeo.com/15424959 & http://vimeo.com/19405046 These videos are based on the Agilent 33220A arbitrary waveform generator. However you may find a Rigol waveform generator (Rigol DG1022) on your lab bench. These two waveform generators have enough differences to warrant this document. Before you use the Rigol DG1022 waveform generator, please view these videos. This document adds to the knowledge presented in the videos. What is a Waveform Generator? A waveform generator is a bench instrument used for generating various time dependent waveforms such as sinusoid, square, and ramp waves. It can also be used to generate DC signals, pulses and modulated signals (explained later in this document). General Interface In this section we introduce the interface of the Rigol DG1022 waveform generator. We do not cover every possible feature of the instrument, instead only the features relevant to the sophomore lab are covered. The front and Rear Panels of Rigol DG1022 are shown in Figs. 1 and 2 respectively. Fig 1. Front panel of the Rigol DG1022 waveform generator Fig 2. Rear panel of the Rigol DG1022 waveform generator In this section we simply explain which part of the interface is used for various functions relevant to the sophomore labs. Later in this document we present more detailed information about the functions mentioned in this section. Power Switches There is a main power switch on the back panel of the wave form generator and a power button at the bottom left hand side corner of the front panel. Main power switch needs to be turned on before you can turn on the waveform generator by pressing the button on the front panel. Soft keys Soft keys are flexibly programmed keys whose functions vary base on the context. On the front panel, a number of soft keys are arranged into functional groups. Menu Keys Menu keys are used to select options displayed on the bottom of the LCD display. Output Channels The waveform generator can output two independent waves corresponding to two channels. Each channel can be set up independent of each other. The upper right hand side of the LCD display shows which channel you are modifying. You can switch the channel to be modified by pressing the “channel switch button”. The two channel outputs are located at the bottom right corner of the front panel. The upper BNC connector (BNC connectors are explained in the lab videos mention above) is for channel 2 and the lower connector is for channel 1. Signal will not appear at the output unless the output button located next to the connector is pressed. The button will turn green when the output is on. It should be noted that channel 2 does not support waveform modulation (explained below). Setting the Parameters There are two ways to change parameters. When a black square is displayed under a numeric digit on the LCD screen then you can rotate the knob to adjust the value of that digit. You can also change the digit by pressing the left/right arrow near the knob. Another way is to enter a number directly from the keypad. Available units associate with the number will appear on the LCD screen as soon as you press on the keypad. Setting the Input Impedance Input impedance for each channel can be set independently. The waveform generator needs to know the input impedance of the LUT (Load Under Test) in order to generate a correct waveform. The impedance can be set through Mode/Functions: Utility ‐> CH1 (or CH2). Setup for Time Dependent Waveforms To set up a time dependent waveform you should first select the waveform type (e.g. sine, square, ramp, pulse, etc) using the waveform keys. Once a waveform type is selected, frequency, amplitude, offset, phase and align phase options will appear on the LCD display for you to adjust individually. View Options Each waveform can be viewed in three different ways: numeric form for the selected channel, graphic form for the selected channel or numeric information for both the channels. Pressing the view button will switch between the three views. Setup for DC voltages To output a DC signal, press Arb ‐> Load ‐> BuiltIn ‐> Others ‐> “DC” and then adjust the DC offset. Setup for AM Modulation Note that only Channel 1 can be used for setting up modulated waves. To set up AM modulation, first a carrier waveform needs to be setup by selecting the waveform type (e.g. sine, square, ramp, pulse, etc) using the waveform keys and setting its properties using the soft keys, then the signal to be modulated is set up by using MOD in mode/functions group. Input and Output Impedances The equivalent circuit of the waveform generator with internal impedance ZS and the Device Under Test (DUT) with input impedance ZL are shown in Fig. 3 below. The internal impedance of the ZS of the waveform generator is equal to 50 ohms. For the waveform generator to output a waveform with the correct amplitude across the load ZL, we need to enter the value of ZL into the signal generator. If the input impedance of the DUT, is very high (infinity) then we should enter a value of “High Z” (infinite impedance) into the wave form generator. Note that in our lab we will set the input impedance of the oscilloscope to 20 Mega Ohms which for all practical purposes can be considered to be infinite impedance. Therefore we will always set the signal generator to “High Z” when we connect it to an oscilloscope. Most devices we connect to the signal generator in our labs will have infinite input impedances. If the input impedance of the DUT equals 50 Ohms then we should enter a value of 50 Ohms into the signal generator. To enter the value of the input impedance go through Modes/Functions: Utility ‐> CH1 (or CH2). You can select “High Z”, 50 Ohms or enter the appropriate value of the impedance of the DUT. Default is “High Z”. AM modulation Amplitude modulation is widely used in the field of communications (this topic will be covered in class lectures). To generate an AM modulation signal we need a carrier sinusoid Ac cos c t . The signal to be modulated will vary the amplitude of the carrier sinusoid proportional to its amplitude. If the signal to be modulated is cos s t , then the AM modulated signal is defined as 1 depth cos s t Ac cos c t where 100 depth is in units of %. Make sure that none of the buttons in Mode/Functions group is lit up. Set up the carrier frequency following normal procedures for setting up waveforms. Then press Mod button in Mode/Functions group. The LCD screen will give you options for Type, SrcExt/SrcInt, Depth, AMFreq and Shape. A typical panel display for modulation setting is as shown below. Type is the type of modulation, i.e., AM, FM, PM or FSK. Press the soft key to enter menu and then use the menu key to select AM. ScrInt means the signal to be modulated is generated internal to the waveform generator. If ScrExt is selected, you can input a signal to be modulated from outside via channel 2. If ScrInt is selected, you can create a signal waveform by setting up the depth of modulation, frequency and shape of the waveform. To set up each of the parameters, use the menu keys to select the parameters and then adjust the value as desired. DC Voltage Generation In some of the labs you will need to generate DC voltage signals from the waveform generator to controls motors. The reason we do not use a DC power supply for this purpose is that a power supply is used for supplying power with large amount of current and is not suitable as a control signal for the motor. To output a DC signal, press Arb ‐> Load ‐> BuiltIn ‐> Others ‐> “DC” and then adjust the DC offset. Reference: Rigol User’s Guide: DG1022 Dual‐Channel Arbitrary/Waveform Generator, June 2010, Rigol Technologies, Inc.