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university:courses:electronics:electronics-lab-19 [29 Dec 2012 19:06] – [Description:] Doug Merceruniversity:courses:electronics:electronics-lab-19 [23 Aug 2019 13:52] (current) – Antoniu Miclaus
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-====== Activity 19. The Switched Capacitor ======+====== Activity: The Switched Capacitor ======
  
 ===== Objective: ===== ===== Objective: =====
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 A switched capacitor is an electronic circuit element used in discrete time signal processing systems. It works by transferring charge into and out of a capacitor when switches are opened and closed. Usually, non-overlapping signals are used to control the switches, often termed Break before Make switching, so that all switches are open for a very short time during the switching transitions. Filters implemented with these elements are termed 'switched-capacitor filters'. Unlike analog filters, which must be constructed with resistors, capacitors and sometimes inductors whose values are accurately known, switched capacitor filters depend only on the ratios between capacitances and the switching frequency. This makes them much more suitable for use within integrated circuits, where the accurately specified absolute value of components such as resistors and capacitors are not economical to construct. A switched capacitor is an electronic circuit element used in discrete time signal processing systems. It works by transferring charge into and out of a capacitor when switches are opened and closed. Usually, non-overlapping signals are used to control the switches, often termed Break before Make switching, so that all switches are open for a very short time during the switching transitions. Filters implemented with these elements are termed 'switched-capacitor filters'. Unlike analog filters, which must be constructed with resistors, capacitors and sometimes inductors whose values are accurately known, switched capacitor filters depend only on the ratios between capacitances and the switching frequency. This makes them much more suitable for use within integrated circuits, where the accurately specified absolute value of components such as resistors and capacitors are not economical to construct.
  
-====== 19.1 The switched capacitor resistor: ======+======  The switched capacitor resistor: ======
  
 The most simple switched capacitor circuit is shown in figure 1, the switched capacitor resistor. It consists of one capacitor C<sub>1</sub> and two switches S<sub>1</sub> and S<sub>2</sub> which connect the capacitor alternately to the input, V<sub>IN</sub> and the output, V<sub>OUT</sub>.  The most simple switched capacitor circuit is shown in figure 1, the switched capacitor resistor. It consists of one capacitor C<sub>1</sub> and two switches S<sub>1</sub> and S<sub>2</sub> which connect the capacitor alternately to the input, V<sub>IN</sub> and the output, V<sub>OUT</sub>. 
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 http://en.wikipedia.org/wiki/Switched_capacitor http://en.wikipedia.org/wiki/Switched_capacitor
  
-====== 19.2 Example Circuit ======+======  Example Circuit ======
  
 The next step is to build an example circuit using the Switched Capacitor as a resistor. By adding a second capacitor C<sub>2</sub> across the output of figure 1, we get the RC low pass circuit shown in figure 2. The next step is to build an example circuit using the Switched Capacitor as a resistor. By adding a second capacitor C<sub>2</sub> across the output of figure 1, we get the RC low pass circuit shown in figure 2.
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 ===== Materials: ===== ===== Materials: =====
-Analog Discovery Lab hardware\\+ADALM2000 Active Learning Module\\
 Solder-less breadboard\\ Solder-less breadboard\\
 Jumper wires\\ Jumper wires\\
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 ===== Directions: ===== ===== Directions: =====
  
-The breadboard connections are as shown in figure 4. If you are using the power supplies from the Discovery hardware be sure that they are turned off while you construct the circuit. The scope inputs should be connected to measure the input and output of the RC filter. The circuit will operate from the +/- 5V supplies provided from the Discovery board but better performance will be observed if a +/- 5V bench power supply is used. A +/- 5V square wave digital signal from AWG2 drives the CD4007 inverter input at pin 6 and the gate of switch devices M<sub>5</sub> and M<sub>6</sub>. The inverted output at pins 8,13 drives the gates of switch devices M<sub>3</sub> and M<sub>4</sub>.+The breadboard connections are as shown in figure 4. If you are using the power supplies from the ADALM2000 hardware be sure that they are turned off or disconnected while you construct the circuit. The scope inputs should be connected to measure the input and output of the RC filter. The circuit will operate from the +/- 5V supplies provided from the ADALM2000 board but better performance will be observed if a +/- 5V bench power supply is used. A +/- 5V square wave digital signal from AWG2 drives the CD4007 inverter input at pin 6 and the gate of switch devices M<sub>5</sub> and M<sub>6</sub>. The inverted output at pins 8,13 drives the gates of switch devices M<sub>3</sub> and M<sub>4</sub>.
  
 {{ :university:courses:electronics:a19_f4.png?550 |}} {{ :university:courses:electronics:a19_f4.png?550 |}}
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 ===== Hardware Setup: ===== ===== Hardware Setup: =====
  
-Waveform generator W1 should be configured as a 100 Hz sine wave with a 500 mV amplitude and zero offset to start out. Waveform generator W2 should be configured as a 100 KHz square wave with a 5 V amplitude and zero offset. Scope channel 1 should be connected to the input of the filter and Scope channel 2 should be connected to the output of the filter. +Waveform generator W1 should be configured as a 100 Hz sine wave with a 1 mV amplitude peak-to-peak and zero offset to start out. Waveform generator W2 should be configured as a 100 KHz square wave with a 10 V amplitude peak-to-peak and zero offset. Scope channel 1 should be connected to the input of the filter and Scope channel 2 should be connected to the output of the filter. 
  
 ===== Procedure: ===== ===== Procedure: =====
  
 Turn on the power supplies and enable both AWG channels. Using the oscilloscope display observe the output amplitude of the filter relative to the input as you change the input frequency, AWG1. Also note any changes in the output amplitude as you change the switching frequency by adjusting the frequency of AWG2. Turn on the power supplies and enable both AWG channels. Using the oscilloscope display observe the output amplitude of the filter relative to the input as you change the input frequency, AWG1. Also note any changes in the output amplitude as you change the switching frequency by adjusting the frequency of AWG2.
-Stop and close the Oscilloscope screen and now open the Network Analyzer instrument ( Bode plotter ). You will need to disable AWG channel 1 on the waveform generator screen but keep channel 2 enabled and set to 100 KHz, 5 V amplitude, zero offset as it was previously. Set up the Analyzer to sweep the filter input from 100 Hz to 10 KHz. Run sweeps with AWG2 set to 100 KHz, 200 KHz and 500 KHz. Export the data for each sweep to a .csv file and using a spreadsheet program like Excel make plots of the amplitude and phase vs. frequency similar to the plots in figure 5 and 6.+Stop and close the Oscilloscope screen and now open the Network Analyzer instrument ( Bode plotter ). You will need to disable AWG channel 1 on the waveform generator screen but keep channel 2 enabled and set to 100 KHz, 10 V amplitude peak-to-peak, zero offset as it was previously. Set up the Analyzer to sweep the filter input from 100 Hz to 10 KHz. Run sweeps with AWG2 set to 100 KHz, 200 KHz and 500 KHz. Export the data for each sweep to a .csv file and using a spreadsheet program like Excel make plots of the amplitude and phase vs. frequency similar to the plots in figure 5 and 6.
  
 {{ :university:courses:electronics:a19_f5.png?550 |}} {{ :university:courses:electronics:a19_f5.png?550 |}}
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 How well do these Bode plot curves match a simple RC low pass filter response? How well do these Bode plot curves match a simple RC low pass filter response?
  
-====== 19.2 Switched capacitor differencing circuit ======+======  Switched capacitor differencing circuit ======
  
 ===== Objective: ===== ===== Objective: =====
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 ===== Procedure: ===== ===== Procedure: =====
  
-Start with AWG1 and AWG2 both set up for sine waves with equal amplitudes of 500 mV and zero offset but with AWG2 set with 180 degree phase. This will result with a differential signal with 1 V amplitude ( 2 V peak to peak ). Observe the signal at the output and record the minimum and maximum values along with the DC ( average ) value of the output.+Start with AWG1 and AWG2 both set up for sine waves with equal amplitudes of 500 mV peak-to-peak and zero offset but with AWG2 set with 180 degree phase. This will result with a differential signal with 2 V amplitude peak-to-peak. Observe the signal at the output and record the minimum and maximum values along with the DC ( average ) value of the output.
  
 Repeat these measurements with the DC offset of both AWG1 and AWG2 set to 250 mV, 500 mV, -250 mV and -500 mV. Repeat these measurements with the DC offset of both AWG1 and AWG2 set to 250 mV, 500 mV, -250 mV and -500 mV.
university/courses/electronics/electronics-lab-19.1356804405.txt.gz · Last modified: 29 Dec 2012 19:06 by Doug Mercer

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