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What are opamps?

Typical Parameters (Amplification Factor and Voltage Gain)

Typical parameters that represent opamp characteristics exist.

Amplification Factor and Voltage Gain

When a voltage is supplied to the input of the amplifier circuit it is multiplied by the amplification factor and appears at the output. This amplification factor is obtained by dividing the output voltage by the input voltage.

With an input voltage Vs,and output voltage Vo, the amplification factor Av is defined by the following formula.

What is a decibel (dB)?

The logarithm of the amplification factor (multiplied by 20) is expressed in units of decibels (dB).
For example, for an opamp with an open gain of 100,000x (105x), the decibel notation will be as follows.


In this way, we can express a large amplification with many multiples of 10 by a smaller number using decibels.
Other units used in analog circuits are shown below.

(a) dB : The logarithm of the ratio of 2 quantities, multiplied by either 10 or 20.

Formula Formula

(b) Vp-p : Difference between the minimum and maximum values of the waveform.

(c) Vrms : Obtained by taking the square root of the mean average of the square of the voltage.

1Vrms = 2√2

(d) dBV : Representation based on 1Vrms

0dBV = 1Vrms

(e) dBm : A reference voltage that gives rise to a power of 1mW for a given load.
Typical load values include 50Ω and 600Ω.

0dBm=0.224Vrms (With a 50Ω load)
0dBm=0.775Vrms (With a 600Ω load)

(f) oct (octave) : 1oct is twice the value for a given frequency.
-6dB/oct indicates that there's a drop of 6db if the frequency is doubled.

(g) dec (decade): 1dec is 10x the value for a given frequency.
-20dB/dec shows that there's a drop of 20dB if the frequency is increased by 10x.
*From (f) and (g),  -6dB/oct= -20dB/dec.

(h) dB (decibel) basic calculation

3dB  ≒ 1.41x ≒ √2
6dB  ≒ 2.00x
10dB ≒ 3.16x
20dB ≒ 10x
ex) 16dB=10dB+6dB → 3.16×2=6.32x

Opamp/Comparator BasicsApplication Notes