Mosfet common source amplifier pspice

Profiles Research Units Publications. Articles Open Access. Amitava Dasgupta. Published in Institute of Physics Publishing. DOI: Volume:

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Content:

• Frequency response of ce amplifier pspice for mac
• Effects of MOSFET mismatch on the performance of single supply low voltage operational amplifiers
• Common Source Amplifier Circuit simulation using LTSpice
• Common Source Amplifier with active load
• Model Library
• MOSFET Common Source Amplifier using PSpice
• Frequency Response for MOSFET/BJT
• PSpice cascode mosfet design not working properly
• Working with MOSFET SPICE Models in Circuit Analyses

WATCH RELATED VIDEO: Transient Analysis of a MOSFET Common Source Amplifier - CS Amplifier - Single stage Amplifier

Frequency response of ce amplifier pspice for mac

Response to a Small Signal - Hz, 0. Every device has slightly different characteristics which must be accounted for in your circuit design. The pSpice simulator encapsulates device measurements such as these in a numerical model, which may comprise many parameters. In the results and plots shown below, we are relying on a numerical model to predict how circuits will work.

This is a remarkably effective approach, widely used by professional designers, but it is vital to remember:. The circuit below entered into pSpice will let us plot out I-V characteristics of the device J1 corresponding to pSpice 's numerical model. It's important to remember, this is a prediction of how a typical device will respond, and not a measurement as such. The data actually entered into pSpice is text-based. The schematic is just for the convenience of a human designer.

Fortunately, it is fairly easy to convert a schematic diagram into data that pSpice can accept. Here's the input that corresponds to the schematic above; it instructs pSpice to plot the drain current in J1 as a function of VDD the drain voltage and VG the gate voltage as these are varied between prescribed limits.

Shown below is the transfer characteristic I D vs. Figure 1a - The Spice I D vs. The topmost curve is for a gate-source voltage of 0V Successive curves have a gate-source step voltage of Now that we have the characteristic I-V plot for the device, we can choose a DC operating point Q for the device. There are a number of factors to consider when picking the operating point for our circuit.

These were covered in Lectures First of all, we want the amplifier to work in a linear region to minimise the amount of signal distortion. The optimum region for the JFET is in the region where the drain current I D is essentially constant, the so-called constant current region. Typically, we will choose an operating point Q that lies near the centroid of the safe region.

Another concern of the circuit designer is power consumption. Since the circuit consumes a certain amount of power even if no signal is connected to the input, typically a designer will wish to minimise the power consumption.

This can be achieved by using as small a drain current as necessary to do the job that the amplifier needs to do. We also want to maximise the output range of our amplifier. If our operating point Q point is too close to earth potential, or to the supply voltage, the signal will clip that is, it will be limited in amplitude by the power supply much sooner then if it were farther away from those two voltages.

For this reason, the device is typically set up to operate at midpoint bias. This means that the JFET is biased so that the drain-source voltage is approximately halfway between the supply voltage and earth potential. In this example, we've chosen an operating point with a drain current of approximately 3 mA and a drain-source voltage of approximately 10 V.

Once the operating point has been chosen, the only other parameter of the circuit is the supply voltage, which was probably already known, and likely a factor in the selection of the operating point. We will use a supply voltage of 20 V. The next step is to draw a line from the X intercept at the supply voltage point, through the operating point Q, all the way to the Y axis.

This is the DC load line, which governs the operation of the circuit, and determines the value we choose for the drain resistor R D. It has slope -RD. The preliminary work is now complete, and we are ready to begin selecting the components necessary to complete the circuit.

To bias the gate at the proper voltage This means that the remaining 10 volts has to be dropped across the drain resistor R D , while a drain current of 3 mA flows.

The design of the circuit is now complete. Applying a sine wave of 0. The self-biassed design allows the bias battery to be eliminated, saving an expensive and bulky battery, at the cost of only one additional resistor RS. From above, to achieve the required operating point, Q, requires the gate electrode to be biased at RG holds the gate at earth potential, or 0 volts, since negligible DC current flows into the gate electrode. Since I D is fixed at 3 mA for the chosen operating point Q, we choose ohms for RS; the closest convenient preferred value is ohms.

The graph below shows the output predicted by pSpice for the self-biassed circuit. Note that the vertical scale for the output lower plot goes from 8V to 12V. Taking into account the the different scaling, the output is now considerably lower than for the battery-biased circuit, with the same input applied. The gain has in fact been reduced, to about Why is this? Because of the presence of the source resistor RS, there is now a fluctuating signal appearing on the source electrode, as the drain current varies.

Consideration of Kirchhoff's voltage law shows that the gate signal voltage v gs is actually reduced below 0. This is an example of negative feedback. Here it is producing an undesired reduction in circuit gain, but properly applied in the right circumstances, negative feedback is an exceedingly powerful technique of immense value in linear circuit design. Fortunately, there is an easy solution to this - see the schematic diagram below. If we connect a bypass capacitor C3 of sufficiently large capacitance in parallel with RS, a bypass path is provided for signal currents to flow directly to earth, rather than through RS; then the full input signal appears between the gate and source, restoring the gain to the expected value.

The crucial service performed by C3 is effectively to short-circuit the source resistor RS for signal frequencies only. However, because no DC current flows through a capacitor, the steady source voltage needed to establish the gate bias to achieve the operating point Q is unaffected.

For the moment, we will sidestep the issue of how to select a 'sufficiently large' value for C3, and we will assume that a value of m F will be satisfactory. Here is a link to the pSpic e circuit schematic file that describes this design. The sine wave response is as shown below, and at the frequency in use, Hz, it can be seen that the gain has been restored to about At this frequency it is apparent that the bypass capacitor C3 uF is adequate.

However, if the frequency were reduced this might not be the case, since capacitive reactance is inversely proportional to frequency. The following simulation run shows how pSpice can be used to show the effect of varying C3, to establish how sensitive is the design's performance to the choice of value. To show the results, we could apply a standard sine wave signal at the input and study the amplitude of the resultant output sine wave.

However, this is rather tedious, and pSpice is capable of interpreting the results for us, actually determining the amplitude of the output. Hence, to see the effect of varying C3 we have pSpice plot output voltage amplitude versus frequency to give a set of frequency response graphs, one for each C3 value.

For this set of results, the input was set to 1 volt p-p, so the vertical scale which represents the p-p output voltage at the drain is numerically equal to the gain.

You can see that the transition between low gain about -4 to high gain about With capacitance of m F, the gain begins to drop off below about 10 Hz. With capacitance of 1 m F the gain begins to drop off below about Hz. The plots have been labelled to show the value of bypass capacitor used.

Note that the frequency scale is logarithmic.

Effects of MOSFET mismatch on the performance of single supply low voltage operational amplifiers

Spice is a program developed by the EE Department at the University of California at Berkeley for computer simulation of analog circuits. In its original form you tell Spice what elements are in the circuit resistors, capacitors, etc. Every node is assigned a number, and there is always a ground node, which is Number 0. Several companies have developed graphical user interfaces for Spice, which make it much easier to use. One of the most popular is PSpice. PSpice provides a free student version of its program which can be downloaded from www. When you start up you will get a screen which looks like this:.

Common Source Amplifier Circuit simulation using LTSpice

I'm making a Common Source amplifier using a mosfet and then comparing that to the same basic setup but with 2 mosfets in cascode. However I get a nearly identical response for both circuits. I believe I've edited the model correctly, but I don't believe I should be getting the same response from both circuits. What am I doing wrong? When I run them trough PSpice I get this output Where Red is the response from the cascode and yellow is the response from the common-source. The cascode transistor improves output impedance to allow a higher voltage gain, but there is no overall improvement since in the first circuit:. Secondly, the cascode bias voltage is probably too high.

Common Source Amplifier with active load

Response to a Small Signal - Hz, 0. Every device has slightly different characteristics which must be accounted for in your circuit design. The pSpice simulator encapsulates device measurements such as these in a numerical model, which may comprise many parameters. In the results and plots shown below, we are relying on a numerical model to predict how circuits will work. This is a remarkably effective approach, widely used by professional designers, but it is vital to remember:.

Model Library

Laboratory experiment using a self-biased common-source JFET amplifier to identify break frequencies, poles and zeros, Bode plots, and common source amplifier characteristics. Procedure: 1. Using the circuit of Figure 1, predict the low frequency break frequencies 4. Modify the circuit to provide the following: a. Draw a Bode plot voltage gain and phase for the modified circuit over a frequency range of 1 Hz to 1 MHz.

MOSFET Common Source Amplifier using PSpice

Transistors are wonderful devices, and it is highly likely that you would not be able to read this sentence on your computer without them. There are many types of transistors, but MOSFETs are by far the most widely used type of transistor used in analog and digital circuits for a variety of applications. So which analyses can you conduct with these different types of models? If you are familiar with the basic ideas of a transistor, then you are aware that any transistor is intended to act like a purely electronic switch with two inputs and one output. Current will flow through the output either into or out of the output, depending on the type of transistor , depending on the potential applied between each input and the output. Note that the gate electrode is insulated from the underlying gate semiconductor by a thin oxide layer. A nonzero source-to-body voltage changes the threshold voltage from its ideal value; this is known as the body effect or back-gate effect.

Frequency Response for MOSFET/BJT

Bill Huffine huffine uscolo. In comparison to the BJT common-emitter amplifier, the FET amplifier has a much higher input impedance, but a lower voltage gain. In this experiment, the student will build and investigate a simple n-channel, common source JFET amplifier. It is assumed that the student has had some background in basic transistor amplifier theory, including the use of simple ac equivalent circuits.

PSpice cascode mosfet design not working properly

Common Source Amplifier : Figure below shows the common source amplifier circuit. In this circuit the MOSFET converts variations in the gate-source voltage into a small signal drain current which passes through a resistive load and generates the amplified voltage across the load resistor. Microelectronic Circuits 5th Edition with PSpice. An inverting amplifier is one which the output is given as feedback to the negative terminal of the operation amplifier.

Working with MOSFET SPICE Models in Circuit Analyses

Figure below shows the circuit diagram of CS amplifier with current source load. The small signal model of this circuit is also shown in Figure below. Ac dc power converters single phase full wave controlled rectifier single phase half wave controlled rectifier three phase full wave controlled rectifier three phase half controlled rectifier. Amplifier instrumentation amplifier inverting amplifier isolation amplifier non inverting amplifier operational amplifier unity gain buffer. Combinational logic circuits arithmetic logic unit binaryaddersubtractor boolean algebra decoders demultiplexers encoders full adder full subtractor half adder half subtractor multiplexer.

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