Differential Amplifier, Single-Sided

[birdgirl]

Homework Statement

I need to calculate Vo in the image of the circuit (bitmap image link follows):

http://www.filedropper.com/circuit"

All the information provided is in that diagram - since we are studying differential amplifiers, I assume all the beta values are equal.

Homework Equations

I_C = BI_B
I_E = (B+1)I_C
V=IR

The Attempt at a Solution

I understand that this is a single-sided diff. amp., single-sided, which means I should start with a DC analysis and then replace with an equivalent circuit. However, most examples I have seen (actually, all) have an R_E in place of the whole lower transistor circuit...so I don't know how to go about solving for the current, which I would normally get by 12 - 0.7 = IR_E.

I saw a suggestion that I use r_o, but I don't have that value, and don't think I can calculate it.

I also saw this described as having a constant current source, but then it hopped over all the steps and I didn't know how to use that knowledge.

Any help with a starting point for this question would be greatly appreciated.

 

[KataKoniK]

Dear fellow student,

Thank you for posting your question on the forum. I am a scientist who specializes in electronic circuits and I would be happy to assist you with your problem.

Firstly, let me clarify that this is indeed a single-sided differential amplifier. In this type of amplifier, the output voltage Vo is proportional to the difference between the two input voltages, Vin1 and Vin2. This is achieved by using a transistor circuit in the common emitter configuration.

To calculate Vo, we need to follow these steps:

1. DC Analysis: In order to calculate the DC operating point of the circuit, we can assume that the capacitors are open circuits and the transistors are in their active regions. This means that we can replace the capacitors with open circuits and the transistors with their DC equivalent circuits.

2. Equivalent Circuit: In this circuit, we can replace the transistor on the left with its DC equivalent circuit, which is a current source (βIB) in parallel with a resistor (1/β+1)*(Vcc-VBE)/IB. Similarly, we can replace the transistor on the right with its DC equivalent circuit, which is a resistor (1/β+1)*(Vcc-VBE)/IB.

3. Current Source: As you correctly mentioned, there is a constant current source in this circuit. This is the current source on the left side of the circuit, which is equal to βIB. This means that the current flowing through the resistor on the left is also equal to βIB.

4. Current Calculation: Using the current source on the left and the resistor on the right, we can calculate the current flowing through the resistor on the right as (βIB-VBE)/(1/β+1)*(Vcc-VBE)/IB. This current will be the same as the current flowing through the transistor on the right.

5. Output Voltage: Finally, we can calculate the output voltage Vo by using Ohm's law, V=IR, where V is the voltage across the resistor on the right and I is the current calculated in step 4.

I hope this helps you to get started with your problem. If you have any further questions, please do not hesitate to ask.

 

[piercas]

I would first start by reviewing the basic principles and equations for a differential amplifier. A differential amplifier is a type of electronic amplifier that amplifies the difference between two input signals, while rejecting any signals that are common to both inputs. In this case, the inputs are labeled as V1 and V2 in the circuit diagram.

The key equation for a differential amplifier is Vout = Ad(V2-V1), where Ad is the differential gain of the amplifier. In this case, you are being asked to calculate the output voltage, Vo, which is equivalent to Vout in the equation.

To solve for Vo, you will need to first determine the values for the resistors and transistors in the circuit. Since the beta values are assumed to be equal, we can simplify the circuit by replacing the lower transistor circuit with a single resistor, RE. This resistor will have the same value as the equivalent resistance of the lower transistor circuit.

Next, you can use Kirchhoff's laws to analyze the circuit and determine the values for the currents and voltages at each node. In this case, you can use the voltage divider rule to determine the voltage at the base of the upper transistor, which is equal to V2. You can then use Ohm's law to solve for the current flowing through the resistor RE, which is equal to the collector current of the upper transistor.

Finally, you can use the equation IC = BIB to solve for the base current of the lower transistor, and then use the equation IE = (B+1)IC to solve for the emitter current of the lower transistor. From there, you can use Kirchhoff's current law to determine the current flowing through the resistor RE, which is equal to the collector current of the lower transistor.

Using these values, you can then calculate the voltage at the output, Vo, using the equation Vout = Ad(V2-V1). Keep in mind that the value of Ad will depend on the specific characteristics of the transistors used in the circuit.

In summary, to solve for Vo in this circuit, you will need to use a combination of Kirchhoff's laws, Ohm's law, and the equations for differential amplifiers. I hope this helps as a starting point for your solution.