100% satisfaction guarantee Immediately available after payment Both online and in PDF No strings attached
Previously searched by you
Electronics 2 study guide with Sample Problems and Solutions to apply the basic principle and concept of Frequency Response of BJT and FET £7.83
Add to cart
- Bipolar transistors are so named because the controlled current must go through
two types of semiconductor material: P and N. The current consists of both
electron and hole flow, in different parts of the transistor.
- Bipolar transistors consist of either a P-N-P or an N-P-N semiconductor
“sandwich” structure.
- The three leads of a bipolar transistor are called the Emitter, Base, and
Collector.
- Transistors function as current regulators by allowing a small current to control a
larger current. The amount of current allowed between collector and emitter is
primarily determined by the amount of current moving between base and emitter.
- In order for a transistor to properly function as a current regulator, the controlling
(base) current and the controlled (collector) currents must be going in the proper
directions: meshing additively at the emitter and going in the direction of the
emitter arrow symbol.
BJT Small Signal Analysis Model
The re and hybrid model will be used to analyse small signal AC analysis of
standard transistor in the region of interest.
,Common Emitter Fixes Bias Configuration
AC Equivalent Ckt
Input Impedance:
𝑍𝑖 = 𝑅𝑠 //𝛽𝑟𝑒
Output Impedance:
𝑍𝑜 = 𝑟𝑜 //𝑅𝑐
If 𝑟𝑜 = ∞,
𝑍𝑜 = 𝑅𝑐
Voltage Gain:
Looking at the output side of AC equivalent circuit,
𝑉𝑜 = −(𝛽𝐼𝑏 )(𝑟𝑜 //𝑅𝑐 )
But
𝑉𝑖
𝐼𝑏 =
𝛽𝑟𝑒
So that
𝑉𝑖
𝑉𝑜 = − (𝛽 ) (𝑟 //𝑅𝑐 )
𝛽𝑟𝑒 𝑜
Therefore
𝑉𝑜 𝑟𝑜 //𝑅𝑐
=−
𝑉𝑖 𝑟𝑒
If 𝑟𝑜 = ∞,
𝑉𝑜 𝑅𝑐
=−
𝑉𝑖 𝑟𝑒
Current Gain:
Applying KCL on the input and output side.
(𝑟𝑜 )(𝛽𝐼𝑏 ) 𝐼𝑜 (𝑟𝑜 )(𝛽)
𝐼𝑜 = 𝑎𝑛𝑑 =
𝑟𝑜 + 𝑅𝑐 𝐼𝑏 𝑟𝑜 + 𝑅𝑐
, (𝑅𝐵 )(𝐼𝑖 ) 𝐼𝑏 (𝑅𝐵 )
𝐼𝑏 = 𝑎𝑛𝑑 =
𝑅𝐵 + 𝛽𝑟𝑒 𝐼𝑖 𝑅𝐵 + 𝛽𝑟𝑒
The result is
𝐼𝑜 𝐼𝑜 𝐼𝑏 (𝑟𝑜 )(𝛽) (𝑅𝐵 )
𝐴𝑖 = = ( )( ) = ( )( )
𝐼𝑖 𝐼𝑏 𝐼𝑖 𝑟𝑜 + 𝑅𝑐 𝑅𝑏 + 𝛽𝑟𝑒
Another formula
𝑉𝑜 𝑉𝑖
𝐼𝑜 = − 𝑎𝑛𝑑 𝐼𝑖 =
𝑍𝑜 𝑍𝑖
The result is
𝐼𝑜 𝑉𝑜 𝑍𝑖 𝑍𝑖
𝐴𝑖 = = (− ) ( ) = −𝐴𝑣
𝐼𝑖 𝑍𝑜 𝑉𝑖 𝑍𝑜
Voltage Divider Bias
AC Equivalent Circuit
Input Impedance
𝑍𝑖 = 𝑅′//𝛽𝑟𝑒
Where
𝑅 ′ = 𝑅1 //𝑅2
Output Impedance
𝑍𝒐 = 𝑟𝑜 //𝑅𝑐
If 𝑟𝑜 = ∞,
𝑍𝒐 = 𝑅𝑐
Voltage Gain
Looking at the output side of AC equivalent circuit,
𝑉𝑜 = −(𝛽𝐼𝑏 )(𝑟𝑜 //𝑅𝑐 )
But
𝑉𝑖
𝐼𝑏 =
𝛽𝑟𝑒
So that
, 𝑉𝑖
𝑉𝑜 = − (𝛽 ) (𝑟 //𝑅𝑐 )
𝛽𝑟𝑒 𝑜
Therefore
𝑉𝑜 𝑟𝑜 //𝑅𝑐
=−
𝑉𝑖 𝑟𝑒
If 𝑟𝑜 = ∞,
𝑉𝑜 𝑅𝑐
=−
𝑉𝑖 𝑟𝑒
Current Gain
Applying KCL on the input and output side.
(𝑟𝑜 )(𝛽𝐼𝑏 ) 𝐼𝑜 (𝑟𝑜 )(𝛽)
𝐼𝑜 = 𝑎𝑛𝑑 =
𝑟𝑜 + 𝑅𝑐 𝐼𝑏 𝑟𝑜 + 𝑅𝑐
(𝑅′)(𝐼𝑖 ) 𝐼𝑏 (𝑅′)
𝐼𝑏 = 𝑎𝑛𝑑 =
𝑅′ + 𝛽𝑟𝑒 𝐼𝑖 𝑅′ + 𝛽𝑟𝑒
The result is
𝐼𝑜 𝐼𝑜 𝐼𝑏 (𝑟𝑜 )(𝛽) 𝑅′
𝐴𝑖 = = ( )( ) = ( )( )
𝐼𝑖 𝐼𝑏 𝐼𝑖 𝑟𝑜 + 𝑅𝑐 𝑅′ + 𝛽𝑟𝑒
Another formula
𝑉𝑜 𝑉𝑖
𝐼𝑜 = − 𝑎𝑛𝑑 𝐼𝑖 =
𝑍𝑜 𝑍𝑖
The result is
𝐼𝑜 𝑉𝑜 𝑍𝑖 𝑍𝑖
𝐴𝑖 = = (− ) ( ) = −𝐴𝑣
𝐼𝑖 𝑍𝑜 𝑉𝑖 𝑍𝑜
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller DocuPlex. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £7.83. You're not tied to anything after your purchase.
