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A short class with Sarah and her students. The other ways are under More.
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Let's start with the common-emitter (CE) amplifier. Can anyone tell me its significance in amplifier circuits?
It's used for voltage amplification, right?
Exactly, it's great for voltage gain! Now, if we look at our previous example, can anyone recall the parameters we used?
We used the supply voltage, transistor beta, and some resistance values.
Correct! We also calculated the collector current. Remember the formula we used for the operating point?
Wasn't it V_CC - V_BE(on) = I_B * R_B?
Right! This leads us to find the collector current. In our case, it was about 2 mA. Great job!
To reinforce this, remember: VAB = IR, where VAB is the voltage across resistors, I is the current, and R is the resistance.
Next, let's talk about small-signal parameters. How do we determine the input resistance of a common-emitter amplifier?
Is it the base resistance plus the gain times the emitter resistance?
Good insight! We can express it as R_in = R_B + β * R_E. Moving on, how did we find the voltage gain?
We used the formula g_m (R_C || r_o), right?
Absolutely! Where g_m is the transconductance. A little mnemonic: GAINS = Gain Amplifier Input Notation Simplified can help remember this.
What was our calculated voltage gain again?
It rounded to approximately 238. Good recall!
Now, let's build on our CE configuration by adding a common-collector (CC) stage. Why do we add this stage?
To increase bandwidth and input resistance, right?
Exactly! When we apply the CC stage, the input resistance notably increases. Can anyone illustrate how we calculate the new emitter current?
From the voltage at the base and emitter voltage, right?
Exactly! We found an emitter current of about 4 mA. Increase in current translates to an increase in bandwidth. Remember: BANDWIDTH = (1/2πRC).
Does adding the CC stage significantly reduce voltage gain?
Good question! Yes, but it enhances bandwidth exponentially! Our gain was roughly 131 post-Cascade.
To wrap this up, summarize how adding the CC stage affects our amplifier's performance.
It lowers the gain a bit but significantly increases the bandwidth!
Correct! We transitioned from 513 kHz to a staggering 10 MHz bandwidth. Remember: BANDS - Bandwidth Achievements Node Demonstrated Success.
So, we can achieve higher frequencies with acceptable gain?
Exactly! This is the power of multi-stage amplifiers. Always account for all configurations!
In circuits wide, CE provides the gain, while CC ensures the bandwidth remains.
Imagine a busy road (CE) that narrows down into a larger highway (CC), allowing more cars (signals) to pass through effortlessly.
For stages, remember: CE’s Gain, CC’s Bandwidth - GBCB.
BANDWIDTH - Bandwidth's Advantage: New Designs Using Transistor Stages Help.
Term
Input Resistance
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Term
Voltage Gain
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A configuration that provides significant voltage gain and is widely used in analog circuits.
A configuration used primarily to increase input resistance and provide impedance buffering.
The ratio of output voltage to input voltage in an amplifier.
A constant value for an amplifier that represents the product of gain and bandwidth.
A measure of the transfer efficiency of the input voltage to output current in a transistor.
This section discusses numerical examples related to multi-transistor amplifiers, focusing on enhancing amplifier bandwidth and input resistance.
The section elaborates on numerical problems involving different multi-transistor configurations such as common-emitter (CE) and common-collector (CC) stages. It demonstrates how these setups can improve bandwidth and input resistance through practical calculations and examples.
In this section, we delve deeper into multi-transistor amplifiers, focusing particularly on practical numerical examples. After reviewing theoretical concepts of mixed configurations, including CE and CC amplifiers, we explore their application through various numerical problems. The main goal is to showcase how modifications in circuit configuration influence the amplifier's performance metrics, including the gain, bandwidth, and input resistance.
Key points covered include:
Common-Emitter (CE) Amplifier:
Common-Collector (CC) Stage:
Performance Summary: