Changes

==Function Generator==

==Function Generator==

A signal generator creates periodic waveforms; it allows the user to manipulate an electrical signal’s amplitude, duty cycle, offset, and frequency over a wide range of values. This signal generator can produce sine, square, triangle, ramp/sawtooth, and digital pulse waveforms. The manual for this signal generator is fairly well-written, so I will only highlight a few excerpts here. I would encourage you to read the manual for complete operating instructions.

A function generator creates periodic waveforms; it allows the user to manipulate an electrical signal’s amplitude, duty cycle, offset, and frequency over a wide range of values. This function generator can produce sine, square, triangle, ramp/sawtooth, and digital pulse waveforms. The manual for this function generator is fairly well-written, so I will only highlight a few excerpts here. I would encourage you to read the manual for complete operating instructions.

[[File:Waveforms.png|400px|thumb|right|Different Waveform Shapes]]

[[File:Waveforms.png|400px|thumb|right|Different Waveform Shapes]]

There are eight range switches that select output frequencies from <1Hz to 10MHz. The coarse frequency knob adjusts the frequency within a range from 10%-of-the-maximum to the maximum. For example, if the 100kHz range is selected, the output frequency can be adjusted from 10kHz to 100kHz. The duty cycle, CMOS level, DC offset, and -20dB functions are only active if their corresponding switches are pressed in. The duty cycle knob alters the symmetry of the waveform through skewing or changing the ratio of “on” time versus “off” time. The DC offset changes the mean amplitude of the waveform. Reference the manual for information on more advanced capabilities such as the sweep functions, TTL/CMOS, and voltage-controlled generation.

There are eight range switches that select output frequencies from <1Hz to 10MHz. The coarse frequency knob adjusts the frequency within a range from 10%-of-the-maximum to the maximum. For example, if the 100kHz range is selected, the output frequency can be adjusted from 10kHz to 100kHz. The duty cycle, CMOS level, DC offset, and -20dB functions are only active if their corresponding switches are pressed in. The duty cycle knob alters the symmetry of the waveform through skewing or changing the ratio of “on” time versus “off” time. The DC offset changes the mean amplitude of the waveform. Reference the manual for information on more advanced capabilities such as the sweep functions, TTL/CMOS, and voltage-controlled generation.

The best way to “see” the output of a function generator is to use an oscilloscope. An oscilloscope will show you a graphical representation of the signal, and allow you to understand the effects of the waveform shape, frequency range switches, coarse/fine adjustment, duty cycle, DC offset, etc.

The best way to “see” the output of a function generator is to use an oscilloscope. An oscilloscope will show you a graphical representation of the signal, and allow you to understand the effects of the waveform shape, frequency range switches, coarse/fine adjustment, duty cycle, DC offset, etc.

A signal generator is designed as a precision device that can produce very specific waveforms; it is not designed as a powering device capable of generating large voltages or currents from its output. This is one of the reasons why a signal generator is commonly used alongside a DC power supply. A common benchtop DC power supply excels at providing a precise DC voltage at a moderate current (usually less than 10A), but it cannot produce waveforms on its own. If you want to produce a waveform with moderate voltage/current, one great method is to design an amplifier circuit. An amplifier circuit commonly uses a transistor (or series of transistors) to turn small low-power signals into larger moderate-power signals. The signal generator provides the small signal to the input of the transistor, which modulates the DC voltage at the output of the transistor to create a larger moderate-power signal.

A function generator is designed as a precision device that can produce very specific waveforms; it is not designed as a powering device capable of generating large voltages or currents from its output. This is one of the reasons why a function generator is commonly used alongside a DC power supply. A common benchtop DC power supply excels at providing a precise DC voltage at a moderate current (usually less than 10A), but it cannot produce waveforms on its own. If you want to produce a waveform with moderate voltage/current, one great method is to design an amplifier circuit. An amplifier circuit commonly uses a transistor (or series of transistors) to turn small low-power signals into larger moderate-power signals. The function generator provides the small signal to the input of the transistor, which modulates the DC voltage at the output of the transistor to create a larger moderate-power signal.

===Impedance===

===Impedance===

Next to the output terminal on the signal generator, it says “50Ω.” This means that the output impedance of the signal generator is 50Ω, which is considered a low output impedance. Impedance is similar in concept to resistance, but it includes additional complex elements that describe a frequency-dependent resistance in AC circuits. A low impedance output offers a couple of options: you can design the input of your circuit for impedance matching (maximum power transfer to the load) or impedance bridging (maximum voltage signal to the load). In this case, impedance matching would mean that the input impedance of your circuit is also at 50Ω. For impedance bridging, the input impedance of your circuit would be much much greater than 50Ω (on the order of kΩ or MΩ). The circuit you’ll be testing in this certification is designed for impedance bridging with the signal generator.

Next to the output terminal on the function generator, it says “50Ω.” This means that the output impedance of the function generator is 50Ω, which is considered a low output impedance. Impedance is similar in concept to resistance, but it includes additional complex elements that describe a frequency-dependent resistance in AC circuits. A low impedance output offers a couple of options: you can design the input of your circuit for impedance matching (maximum power transfer to the load) or impedance bridging (maximum voltage signal to the load). In this case, impedance matching would mean that the input impedance of your circuit is also at 50Ω. For impedance bridging, the input impedance of your circuit would be much much greater than 50Ω (on the order of kΩ or MΩ). The circuit you’ll be testing in this certification is designed for impedance bridging with the function generator.

Why mention all this business about impedance? This will help you know what to expect from the signal generator and how to design circuits better. In the manual, it states, “Remember that the output signal swing of the generator is limited to ±10V open circuited or ±5V into 50Ω, and applies to the combined peak-to-peak signal and DC offset. Clipping occurs slightly above these levels.” This means that if the signal generator is impedance bridged with your circuit, don’t expect to generate signals outside of a ±10V range. If the signal generator is impedance matched with your circuit, don’t expect to generate signals outside of a ±5V range. This includes the DC offset in both cases. If your input impedance falls anywhere between 50Ω and an open circuit (∞Ω), the maximum signal you can get from the signal generator will fall between ±5V and ±10V, respectively. Unless you really know what you are doing, do not use the signal generator on circuits that have an input impedance of less than 50 Ω. Similarly, do not choose an injection point in your circuit for the signal generator that has a DC voltage higher than what can be achieved with the DC offset knob. Only choose injection points where the DC voltage can be matched with the DC offset knob; otherwise, this can cause internal damage to the signal generator.

Why mention all this business about impedance? This will help you know what to expect from the function generator and how to design circuits better. In the manual, it states, “Remember that the output signal swing of the generator is limited to ±10V open circuited or ±5V into 50Ω, and applies to the combined peak-to-peak signal and DC offset. Clipping occurs slightly above these levels.” This means that if the function generator is impedance bridged with your circuit, don’t expect to generate signals outside of a ±10V range. If the function generator is impedance matched with your circuit, don’t expect to generate signals outside of a ±5V range. This includes the DC offset in both cases. If your input impedance falls anywhere between 50Ω and an open circuit (∞Ω), the maximum signal you can get from the function generator will fall between ±5V and ±10V, respectively. Unless you really know what you are doing, do not use the function generator on circuits that have an input impedance of less than 50 Ω. Similarly, do not choose an injection point in your circuit for the function generator that has a DC voltage higher than what can be achieved with the DC offset knob. Only choose injection points where the DC voltage can be matched with the DC offset knob; otherwise, this can cause internal damage to the function generator.

===Using a Function Generator===

===Using a Function Generator===