Direct-coupled amplifier
A direct-coupled amplifier or DC amplifier is a type of amplifier in which the output of one stage of the amplifier is coupled to the input of the next stage in such a way as to permit signals with zero frequency, also referred to as direct current, to pass from input to output.(Bondad M.L., 2016, BSEE)
Current
The common use of the term "AC amplifier" does not mean "direct current amplifier", as this type can be used for both direct current and alternating current signals. The frequency response of the direct coupled amplifier is similar to low pass filter and hence it is also known as "Low-Pass Amplifier". The amplification of DC (zero frequency) is possible only by this amplifier, hence it later becomes the building block for differential amplifier and operational amplifier. Furthermore, monolithic integrated circuit technology does not allow the fabrication of large coupling capacitors.
Advantages
There are several advantages of using this type of amplifier, including:
- Simple circuit arrangement as there are minimum number of components
- For above reason, also quite inexpensive
- Can be used to amplify zero and low frequency signals
Disadvantages
In addition to the advantages, there are also several known disadvantages. These include:
- In dc amplifier DRIFT is observed, which is an unwanted change in output voltage without change in input voltage.
- The output changes with the age or time and change in supply voltage.
- Transistor parameter like vbe and β changes with temperature. this causes change in collector current and voltage. Therefore, the output voltage changes
- Any noise or stray pickup appearing at the input of the amplifier increases at the output, due to the high gain.
Application
Direct-coupled amplifiers are used in TV receivers, computers, regulator circuits and other electronic instruments. It also forms a building block for differential amplifiers and operational amplifiers.