coupling capacitors are generally used to couple the the AC component of voltage to the DC component(biased voltage) of the transistor amplifier .
As we know that the capacitor itself has some reactance which is variable with the applied frequency
Rc=1/wc
where w=frequency in radians
= 2*pi*f
and f= frequency of circuit.
and, V=VC+VIN
VC= voltage drop on capacitor
VIN= resultant voltage available for the transistor for amplification
so as,
frequency increases
reactance decreases
drop on C decreases
so, voltage available for transistor increases
and now you can analyse yourself for the case if frequency decreases
All amplifier typically exhibit a band-pass frequency response. The cut off frequency in the low end is usually determined by the coupling band bypass capacitor .and the high frequency limit is typically determined by internal capacitances in the transistor itself.
Direct coupling
It can take a lot of capacitance to present a low impedance to a low frequency. Electrolytics offer lots of capacitance for a low price.
Quite simply, it's an amplifier wherein the stages as set up so that the output of one stage is coupled directly into the input of the next stage without any wave shaping or tuninig components between them. This makes for fairly flat frequency response. A link is provided to the Wikipedia article on direct coupling.
Probably vacuum ac capacitors.
All amplifier typically exhibit a band-pass frequency response. The cut off frequency in the low end is usually determined by the coupling band bypass capacitor .and the high frequency limit is typically determined by internal capacitances in the transistor itself.
Direct coupling
It can take a lot of capacitance to present a low impedance to a low frequency. Electrolytics offer lots of capacitance for a low price.
Merit: RC-coupled amplifiers are simple and inexpensive to design and construct, providing good frequency response over a wide range of frequencies. Demerit: They have limited low-frequency response due to the capacitive coupling, which can result in signal attenuation at lower frequencies. Additionally, they may suffer from coupling capacitor leakage, affecting the overall performance of the amplifier.
presence of capacitors
frequency response curve helps us to find the bandwidth of particular amplifier circuit. Bandwidth is the range of frequency at which the amplifier works better....
As the frequency of an amplifier increases, the gain decreases due to the capacitive reactance of the internal components. Capacitors start to act as a short circuit at high frequencies, causing the signal to bypass the amplification stage and reducing the overall gain. This phenomenon is known as the frequency response of the amplifier.
Quite simply, it's an amplifier wherein the stages as set up so that the output of one stage is coupled directly into the input of the next stage without any wave shaping or tuninig components between them. This makes for fairly flat frequency response. A link is provided to the Wikipedia article on direct coupling.
Probably vacuum ac capacitors.
all reactive elements in the amplifier, including stray capacitances and inductances.
Rc coupled amplifier is used where good frequency response required. in case of multistage amplification system,To prevent resistance of one stage to come in parallel with next stage, it is used. we use capacitor as a coupling element between two consecutive stages.
RC COUPLING :- is the most Commonly used Coupling Between the two stages of a cascaded or multistage amplifier because it is cheaper in cost and Very compact circuit and provides excellent frequency response. TRANSFORMER COUPLING :- Impedence Coupling results in more efficient amplification because no signal power is wasted in Inductor L. Such Coupling has the drawback of being larger, Heavier and Costlier than the RC COUPLING. Impedence Coupling is rarely used beyond audio range . by : Muhammad zubair.... muet student of telecom.