How to determine the frequency of a circuit?

[ericmar]

Hi,

May I know which is the main thing to determine the frequency of a circuit? How to classify which category of the frequency falls in? Like wat range is considered High Freq? Low Freq?

Thanks.

Sincerely,
Eric

 

[v_c]

I think the term to be used here is "frequency response".
This is normaly described by the transfer function of the circuit.
However, it should be noted that there are many transfer functions
of a given circuit since transfer function in general is the ratio
of a response to a given excitation. This excitation is usually
a small-signal ac excitation and response is the measured ac signal.

If you excite the circuit with a voltage at the input and
measure the response at the output, this will be the voltage gain
transfer function. If you excite the circuit with a current at the
input and measure the input voltage as the response, then the
transfer function is the input impedance. As I said, there are many more.

Transfer function is usually plotted as a magnitude versus frequency
and from the shape of this plot you may be able to classify the frequency
characteristics as lowpass, bandpass, highpass, etc.

If the circuit is linear, then you just have to use Laplace transformed
circuit elements and derive the transfer function. If the circuit is nonlinear
you must first linearize around an operating point to derive the transfer
function, since transfer function is really only valid for linear or linearized systems.

Just do a google search on "transfer function" and/or "frequency response"
related to circuits and you will find lots of material.

Best regards,
v_c

 

[docel]

Sound Waves:
Audio Frequency AF =20Hz to 20000Hz.
Ultrasonic: 18000Hz to ~1MHZ

Radio Waves {Electromagnetic Spectrum}:
Low frequency LF 5 30–300 kHz
Medium frequency MF 6 300–3000 kHz
High frequency HF 7 3–30 MHz
Very high frequency VHF 8 30–300 MHz
Ultra high frequency UHF 9 300–3000 MHz
Super high frequency SHF 10 3–30 GHz
Extremely high frequency EHF 11 30–300 GHz

 

[amriths04]

if you have any frequency dependant component then on knowing its gain bandwidth product you can determine that at what frequency the circuit is operating by knowing the gain at that specific point, for the g-bw is constant throughout for a linear circuit amplifier.

regards,

 

[Monkey_lixueling]

You can derive the mathematic represention using the ideal model of electrical component!