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IFD:Analog Circuits and Interfaces/introduction to electronics (view source)
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* We can use a special configuration of the Opamp together with a capacitor as a simple oscillator. The following simulation is a square wave oscillator. At the positive input terminal, there is a voltage divider, that divides down the output of the opamp in half. Since it is positive feedback, the opamp will drive to the maximum point, which in our case is +-15V. The voltage divider divides this voltage down to half. Depending on whether the output drives high or low, the voltag at the positive input is thus +-7.5V. The capacitor gets constantly charged and discharged from the output of the opamp through the resistor. The voltage at the capacitor on the negative input compares to this threshold voltage and inverts the signal when it exceeds the respective treshold. Since this process is endlessly repeating, the output oscillates. The frequency is dependend on the size of the capacitor and the resistance of the negative feedback resistor. | * We can use a special configuration of the Opamp together with a capacitor as a simple oscillator. The following simulation is a square wave oscillator. At the positive input terminal, there is a voltage divider, that divides down the output of the opamp in half. Since it is positive feedback, the opamp will drive to the maximum point, which in our case is +-15V. The voltage divider divides this voltage down to half. Depending on whether the output drives high or low, the voltag at the positive input is thus +-7.5V. The capacitor gets constantly charged and discharged from the output of the opamp through the resistor. The voltage at the capacitor on the negative input compares to this threshold voltage and inverts the signal when it exceeds the respective treshold. Since this process is endlessly repeating, the output oscillates. The frequency is dependend on the size of the capacitor and the resistance of the negative feedback resistor. | ||
[http://www.falstad.com/circuit/circuitjs.html?cct=$+1+0.000005+12.050203812241895+54+5+43%0Ag+-240+96+-240+112+0%0Ax+-134+-188+297+-185+4+18+Self-Oscillating%5CsComparator%5Cs(Square%5CsWave%5CsGenerator)%0Aa+-240+0+-128+0+8+15+-15+1000000+6.090293760309295+7.500070481327725+100000%0Aw+-128+0+-96+0+0%0Ag+-304+-16+-304+0+0%0A207+-96+0+-48+0+4+output%0Ac+-304+-16+-240+-16+0+1.0000000000000001e-7+-6.090293760309295%0Ar+-240+48+-240+96+0+100000%0Ar+-240+48+-128+48+0+100000%0Aw+-240+16+-240+48+2%0Aw+-128+0+-128+48+0%0Ar+-240+-64+-128+-64+0+100000%0Aw+-128+-64+-128+0+0%0Aw+-240+-64+-240+-16+2%0Ao+9+64+0+4098+10+0.00009765625+0+2+9+3%0Ao+13+64+0+4098+10+0.00078125+1+2+13+3%0A Square Wave Generator] | [http://www.falstad.com/circuit/circuitjs.html?cct=$+1+0.000005+12.050203812241895+54+5+43%0Ag+-240+96+-240+112+0%0Ax+-134+-188+297+-185+4+18+Self-Oscillating%5CsComparator%5Cs(Square%5CsWave%5CsGenerator)%0Aa+-240+0+-128+0+8+15+-15+1000000+6.090293760309295+7.500070481327725+100000%0Aw+-128+0+-96+0+0%0Ag+-304+-16+-304+0+0%0A207+-96+0+-48+0+4+output%0Ac+-304+-16+-240+-16+0+1.0000000000000001e-7+-6.090293760309295%0Ar+-240+48+-240+96+0+100000%0Ar+-240+48+-128+48+0+100000%0Aw+-240+16+-240+48+2%0Aw+-128+0+-128+48+0%0Ar+-240+-64+-128+-64+0+100000%0Aw+-128+-64+-128+0+0%0Aw+-240+-64+-240+-16+2%0Ao+9+64+0+4098+10+0.00009765625+0+2+9+3%0Ao+13+64+0+4098+10+0.00078125+1+2+13+3%0A Square Wave Generator] | ||
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[[file: square_wave_oscillator.png]] This is the breadboard version of the square wave oscillator. The output frequency should be around 50-100Hz. You can connect this to a small speaker or headphone directly. To connect it to a Hifi amplifier input, you need to convert the output voltage from around +-4V to +-1V by using a voltage divider. | [[file: square_wave_oscillator.png]] This is the breadboard version of the square wave oscillator. The output frequency should be around 50-100Hz. You can connect this to a small speaker or headphone directly. To connect it to a Hifi amplifier input, you need to convert the output voltage from around +-4V to +-1V by using a voltage divider. | ||
== Filters == | |||
* To shape the spectrum of our oscillators we will use a lowpass filter. The simplest form of a lowpass filter is the passive lowpass filter. You can view this lowpass filter as an elaborated voltage divider: the capacitor has a frequency dependent resistance (which we call an impedance). This impedance is very high for static voltages (DC) and low frequencies. The impedance goes down the higher the frequency is at its input. The higher the frequency, the lower the impedance at the capacitor and the lower will be the voltage at the capacitor. This will effectively filter out high frequencies and leave lower frequencies in the signal. | * To shape the spectrum of our oscillators we will use a lowpass filter. The simplest form of a lowpass filter is the passive lowpass filter. You can view this lowpass filter as an elaborated voltage divider: the capacitor has a frequency dependent resistance (which we call an impedance). This impedance is very high for static voltages (DC) and low frequencies. The impedance goes down the higher the frequency is at its input. The higher the frequency, the lower the impedance at the capacitor and the lower will be the voltage at the capacitor. This will effectively filter out high frequencies and leave lower frequencies in the signal. | ||