Amplify an Analog Signal

The two main types of direct coupled amplifiers are linear and digital. A linear amplifier has a frequency range where the output signal is linearly amplified relative to the input signal, and a non-linear frequency range. Linear amplifiers are categorized into Class-A, Class-B, and Class-AB. more..

LCM6482 Op-Amp

The difference amplifier can be configured to linearly scale and offset an analog voltage. The circuit in the image below is a difference amplifier where the input from 0.5 to 4.5 V is linearly scaled down to 0.2 to 3.3 V.

The difference amplifier output is:


Vo=G∗(Vin−K)

G is the gain
K is the offset

G & K are found by:

3.3 = G * (4.5 - K)     equation 1
0.2 = G * (0.5 - K)     equation 2

Subtracting the two equations:

3.1 = G * (4)
G = 3.1/4 = 0.775

The gain needed is 0.775

Substituting the gain G back into equation 1 and solving for K:

3.3 = 0.775 * (4.5 - K)
K = 4.5 - (3.3/0.775) = 0.24 V

The ratio of R2/R3 = R4/R1 = 0.775. Typically R2 = R4, and R3 = R1. Here is how to choose more common resistor values for R3 and R2:


Let R3 = 470 k Ohms
R2 = 470000 * 0.775 = 364 k Ohms, so use the more common 360 k Ohm resistor with 1.1% difference

IMPORTANT: Make sure to use precision resistors with 1% or less tolerance since that 1% tolerance in addition to the 1.1% rounding could be a larger difference in actual circuit gain. (360000 * (1 - 0.001) = 359,640 Ohms. 470000 * (1 + 0.001) = 470,470 359640/470,470 = 0.764 (0.775 - 0.764) / 0.775 = 1.4% error)

In order to create the offset K = 0.24 V, a voltage divider is used to device the 3.3V down to 0.24 V.


Voltage divider ratio for R6/R5 = (3.3 - 0.24) / 0.24 = 12.75

Let R5 = 3.3 k Ohms
R6 = 12.75 * 3300 = 42 k Ohms

TLV2462 Op-Amp

The Op Amp TLV2462 can be purchased from Adafruit. It has two amplifiers inside. Supply voltage can be between 2.7 and 6.0 V, 6 MHz gain bandwidth, and 1.6 V/us slew so you can drive fairly fast signals . It can push up to 80 mA. datasheet

The recessed depression in ths surface of the chip points to pin 1.

Application Circuit

The above circuit uses a TLV2462 Op Amp to amplify the US5881LUA hall effect sensor output from 0.022 V to 0.5 V (0.4 V range) to 1.2 to 3.3 V (2.1 V) range. If the TLV2462 Op Amp is powered by 5.0 V, then the output is 1.6 to 5.0 V (3.4 V) range.

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