t
= 1.2/10 ï¿½ 10-3
The bandwidth for current or voltage amplifiers is defined as the range of frequencies at which the gain does not drop down further than 70.7%. The cut-off frequencies are the points at which fulfil the requirements for the amplifier gain. Below is a typical frequency response curve:
The bandwidth is calculated using the formula:
Bandwidth = Upper cut-off frequency – Lower cut-off frequency
Upper cut-off frequency: 21kHz
Lower cut-off frequency: 29Hz
Bandwidth = 21000 – 29
= 20971Hz or 20.97kHz
The bandwidth of the circuit amplifier is 20.97kHz
SECTION B (2a) – Specific function of two different types of transistor within a genuine circuit
1. Metal Oxide Semiconductor Field Effect Transistor (MOSFET)
Below is a diagram of a typical MOSFET common-source amplifier. Low power MOSFETs are useful for radio frequency circuits. This is because they have a rapid response time. Amplifiers based on power MOSFETs are useful for power-control circuits. They have better thermal stability than bipolar transistors (less subject to thermal runaway).
2. Unijunction Transistor (UJT)
This is one of the simplest oscillator circuits based on a unijunction transistor. In the above circuit, the potential difference across the capacitor gradually builds up and is released almost instantly. This type of oscillator is known as a ‘relaxation oscillator’.