TS616IDWT datasheet(24/37 Pages) STMICROELECTRONICS

24 / 37 page

Noise measurements

TS616

24/37

The output noise eNo is calculated using the Superposition Theorem. However eNo is not

the sum of all noise sources, but rather the square root of the sum of the square of each

noise source, as shown in Equation 1.

Equation 1

Equation 2

The input noise of the instrumentation must be extracted from the measured noise value.

The real output noise value of the driver is:

Equation 3

The input noise is called the Equivalent Input Noise as it is not directly measured but is

evaluated from the measurement of the output divided by the closed loop gain (eNo/g).

After simplification of the fourth and the fifth term of Equation 2 we obtain:

Equation 4

7.1

Measurement of eN

If we assume a short-circuit on the non-inverting input (R3=0), Equation 4 becomes:

Equation 5

In order to easily extract the value of eN, the resistance R2 will be chosen as low as

possible. On the other hand, the gain must be large enough:

●

R1=10

Ω, R2=910 Ω, R3=0, Gain=92

●

Equivalent input noise: 2.57 nV/

√Hz

●

Input voltage noise: eN=2.5 nV/

√Hz

NoV1

+++

iNn

iNp

…

--------

⎝⎠

⎛⎞

4kTR1

4kTR2

--------

⎝⎠

⎛⎞

4kTR3

eNo

Measured

()

instrumentation

()

–

iNn

iNp

×… g4kTR2

--------

⎝⎠

⎛⎞

4kT

NoeN

iNn

g4kTR2

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