Table of Contents
Can we use BJT as an amplifier?
Bipolar junction transistors (Also known as BJTs) can be used as an amplifier, filter, rectifier, oscillator, or even a switch, which we cover an example in the first section. The transistor will operate as an amplifier or other linear circuit if the transistor is biased into the linear region.
Can a transistor be used as a filter?
Although operational amplifiers are able to form the basis of an active high pass filter, a single transistor is also able to provide the same function with very acceptable performance.
What components are required to create an active filter?
As their name implies, Active Filters contain active components such as operational amplifiers, transistors or FET’s within their circuit design. They draw their power from an external power source and use it to boost or amplify the output signal.
Why FET op-amp is better than BJT op-amp?
The input impedance at the gate of an FET is very high, unlike the BJT, which comparatively has much lower impedance. Additionally, the conductivity of the channel depends on the voltage applied to the Gate, essentially making it a voltage-controlled device, unlike the BJT, which is current-controlled.
In which mode BJT works as an amplifier?
The most common function of a transistor is to be used in COMMON EMITTER mode. In this method of connection small changes in base/emitter current cause large changes in collector/emitter current. Therefore the circuit is that of a CURRENT amplifier.
How do you create an active filter?
To design filters, the specifications that need to be established include:
- The range of desired frequencies (the passband) together with the shape of the frequency response.
- Input and output impedance requirements.
- Dynamic range of the active elements.
- The degree to which unwanted signals should be rejected.
How to apply active filters to BJTs?
The easiest approach is to take filters designed for op-amps configured at unity gain, (as in your second schematic), and apply them directly to BJTs in emitter follower configuration (as in your first schematic). In order to answer this question, we first have to get an overview of the different principles for realizing active filters:
What is the difference between passive and active low pass filters?
Active Low Pass Filter The most common and easily understood active filter is the Active Low Pass Filter. Its principle of operation and frequency response is exactly the same as those for the previously seen passive filter, the only difference this time is that it uses an op-amp for amplification and gain control.
Why do op amps have JFETs and BJTs in them?
Some op amps (for example, the TL074 or the LF357) use a mixture of JFETs and BJTs to achieve better characteristics in some respects than a bipolar-only design. (JFETs are preferred over MOSFETs due to their greater resilience when it comes to brief overloads and static discharges.)
What are the different first-order active low pass filter circuit configurations?
Examples of different first-order active low pass filter circuit configurations are given as: Here the capacitor has been moved from the op-amps input to its feedback circuit in parallel with R2. This parallel combination of C and R2 sets the -3dB point as before, but allows the amplifiers gain to roll-off indefinitely beyond the corner frequency.