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in fact coupling capacitor is used to block DC voltage from pathing to the next stage of the amplifier
if we connect stages of amplifiers directly; the may enter saturation region because the DC make level shifting and then make clipping in the amplified signal (i.e. distorsion)
Decoupling cap is normally used as LPF to attenuate the noise, normally connected between VDD/VSS, bypass cap function almost the same, but connected to signal to vss/vdd
1. Coupling capacitor is used for blocking D.C. to the next stage and together with other dump and distributed component forming filter characteristic. But in instrument amplifier which needs very low frequency or D.C. (Direct Current) application will use Direct Coupling (D.C)
2. Bypass capacitor is used to bypass the A.C. signal to ground which is called A.C. ground.
Coupling capacitor are actually to bloqing de DC signal from the previous stage (bias voltage) and allowing AC (information) information to the nex stage.
Bypass capacitor are to send noise or fluctuations from DC source to ground, these fluctuations are produced by the operation of the CI or the circuit.
From ac analysis method, coupling capacitor normaly will introduce a zero to the whole circuit. in contrast, bypass capacitor will introduce a pole to the whole circuit.
Hi Migueal,
Can you further elaborate on bypass capacitor? I am interested in the statement you mentioned: " Bypass capacitor are to send noise or fluctuations from DC source to ground"
Is Bypass Capacitor applicable on an ADC input line?
Will it jeopardize the measurement accuracy? I am having a problem in ADC measuring in 20uA range, it seems that there are too "noisy" in the ADC input line.
Where can I get more in for on the bypassing capacitor?
One of basic properties of bypass capacitor is it's low reactance in respect to frequency of AC signal. The effect of placing such capacitor across supply rails, for example, reduces noise or ripple on supply voltage. Supply voltage source has a finite internal resistance and the AC component of load current causes noise or ripple on it. Bypass capacitor lowers this internal resistance for AC.
Because of specific properties of capacitors for example ESR and inductance for wideband bypassing we use parallel connected capacitors with different capacitances. The most often example is use of 10-100uF electrolitic capacitor and 100nF capacitor in parallel across supply.
Is Bypass Capacitor applicable on an ADC input line?
Will it jeopardize the measurement accuracy? I am having a problem in ADC measuring in 20uA range, it seems that there are too "noisy" in the ADC input line.
Yes, it will influence your accuracy. Make sure you have at least a ground line twisted with your ADC input, or better still, a shielded cable. Also try to make the distance as short as you can. Probably this line is picking up the noise. If the frequency of the noise, and the frequency of your signal differ by a fair bit, you could then make a filter with a resistor and capacitor to attenuate the noise, but I would look at shielding first.
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