Consider the following circuit: V(t) Vin 20 V(t) +1. The portion inside the dotted line is...

 

Transcribed Image Text:

Consider the following circuit: V(t) Vin 20 V(t) +1. The portion inside the dotted line is the amplifier; typically amplifiers have external connections for the input signal, the output signal, the power supply and the ground reference. The symbol at the right is the block diagram for a voltage amplifier. Typically the power and ground connections are omitted because they just clutter up the diagram and everyone knows that they must be there. There are many different combinations of components that could be inside the dotted line and they would still be represented by the same signal on a block diagram, for instance you could represent one channel of a stereo amplifier like this. a) For the drain resistor Rp 100 Ohms, gm = 0.3 mhos, and an input source V(t) = Acos(2nft) where A is 20 mV and the frequency is 440 Hz (this is the frequency of the first A above middle C on a piano and serves as a general tuning standard for musical pitch), find an expression for the current, through Rd as a function of time, i (t)=?. 2 Vout RD Vout Vin Vad Vout 18mVgs Vad b) Given your expression for i(t), find an expression for the voltage drop across the resistor Rd as a function of time, Vr(t) =?. c) Now, you can determine the gain by calculating the ratio Vr(t)/Vin(t). This is the ratio of the voltage change at the output to the voltage change at the input. (Notice that when the voltage rises at the input it falls at the output, to handle this we usually refer to this as having a negative gain, a technicality that here we will conveniently ignore.) d) What is the gain of this amplifier if instead of using one transistor you instead make it using two of these transistors wired in parallel like this: V(t) RD V(t) Vin Vout RD Where the gates of the two transistors have been connected to each other, the drains have been connected together as have the sources. -11. Vout Vad + Vad e) Finally redesign the original amplifier so that you have a voltage gain of 100 by choosing a different value for Rd. (Hint this is easier to do if you first derive a symbolic expression for the gain and then plug in values). You can't keep playing this game forever because the signal cannot swing higher than the positive supply or lower than ground for this amplifier. Consider the following circuit: V(t) Vin 20 V(t) +1. The portion inside the dotted line is the amplifier; typically amplifiers have external connections for the input signal, the output signal, the power supply and the ground reference. The symbol at the right is the block diagram for a voltage amplifier. Typically the power and ground connections are omitted because they just clutter up the diagram and everyone knows that they must be there. There are many different combinations of components that could be inside the dotted line and they would still be represented by the same signal on a block diagram, for instance you could represent one channel of a stereo amplifier like this. a) For the drain resistor Rp 100 Ohms, gm = 0.3 mhos, and an input source V(t) = Acos(2nft) where A is 20 mV and the frequency is 440 Hz (this is the frequency of the first A above middle C on a piano and serves as a general tuning standard for musical pitch), find an expression for the current, through Rd as a function of time, i (t)=?. 2 Vout RD Vout Vin Vad Vout 18mVgs Vad b) Given your expression for i(t), find an expression for the voltage drop across the resistor Rd as a function of time, Vr(t) =?. c) Now, you can determine the gain by calculating the ratio Vr(t)/Vin(t). This is the ratio of the voltage change at the output to the voltage change at the input. (Notice that when the voltage rises at the input it falls at the output, to handle this we usually refer to this as having a negative gain, a technicality that here we will conveniently ignore.) d) What is the gain of this amplifier if instead of using one transistor you instead make it using two of these transistors wired in parallel like this: V(t) RD V(t) Vin Vout RD Where the gates of the two transistors have been connected to each other, the drains have been connected together as have the sources. -11. Vout Vad + Vad e) Finally redesign the original amplifier so that you have a voltage gain of 100 by choosing a different value for Rd. (Hint this is easier to do if you first derive a symbolic expression for the gain and then plug in values). You can't keep playing this game forever because the signal cannot swing higher than the positive supply or lower than ground for this amplifier.

Answer rating: 100% (QA)

SOLUTION a To find the expression for the current through resistor R we can use Ohms Law and the rel... View the full answer