TS616IDW(2002) データシートの表示（PDF） - STMicroelectronics
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TS616IDW Datasheet PDF : 27 Pages
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TS616
NOISE MEASUREMENT
Figure 62: Noise Model
R3
iN+
+
TS616
_
N3 iN- eN
N2
R2
R1
N1
output
HP3577
Input noise:
8nV/√Hz
eN : input voltage noise of the amplifier
iNn : negative input current noise of the amplifier
iNp : positive input current noise of the amplifier
The closed loop gain is :
AV = g = 1 + R--R---f-g-b--
The six noise sources are :
V1 = eN × 1 + RR-----21-
V2 = iNn × R2
V3 = iNp × R3 × 1 + RR-----21-
V4 = –RR-----21- × 4kTR1
V5 = 4kTR2
V6 = 1 + RR-----21- 4kTR3
We assume that the thermal noise of a resistance
R is:
4kTR∆F
wher ∆F is the specified bandwidth.
On 1Hz bandwidth the thermal noise is reduced to
4kTR
k is the Boltzmann’s constant, equal to
1,374.10-23J/°K. T is the temperature (°K).
The output noise eNo is calculated using the Su-
perposition Theorem. However it is not the simple
sum of all noise sources. The square root of the
sum of the square of each noise source.
eNo = V12 + V22 + V32 + V42 + V52 + V62,(eq1)
2
eNo
=
2
eN
×
2
g
+
2
iNn
×
2
R2
+
2
iNp
×
2
R3
×
2
g
…
+
RR-----21-
2
×
4kTR1
+
4kTR2
+
1
+
RR-----21-
2
×
4 k T R 3,
(eq2)
The input noise of the instrumentation must be ex-
tracted from the measured noise value. The real
output noise value of the driver is:
eNo = (Measured)2 – (instrumentation )2, (eq3)
The input noise is called the Equivalent Input
Noise as it is not directly measured but it is evalu-
ated from the measurement of the output divided
by the closed loop gain (eNo/g).
After simplification of the fourth and the fifth term
of (eq2) we obtain:
eNo2 = eN2 × g2 + iNn2 × R22 + iNp2 × R32 × g2
… + g × 4kTR2 + 1 + RR-----21- 2 × 4kTR3, (eq4)
Measurement of eN:
We assume a short-circuit on the non-inverting in-
put (R3=0). (eq4) comes:
eNo =
2
eN
×
2
g
+
2
iNn
×
2
R2
+
g
×
4 k T R 2,
(eq5)
In order to easily extract the value of eN, the resis-
tance R2 will be chosen as low as possible. In the
other hand, the gain must be large enough.
R1=10Ω, R2=910Ω, R3=0, Gain=92
Equivalent Input Noise: 2.57nV/√Hz
Input Voltage Noise: eN=2.5nV/√Hz
Measurement of iNn:
R3=0 and the output noise equation is still the
(eq5). This time the gain must be decreased to de-
crease the thermal noise contribution.
R1=100Ω, R2=910Ω, R3=0, Gain=10.1
Equivalent Input Noise: 3.40nV/√Hz
Negative Input Current Noise: iNn =21pA/√Hz
Measurement of iNp:
To extract iNp from (eq3), a resistance R3 is con-
nected to the non-inverting input. The value of R3
must be chosen in order to keep its thermal noise
21/27
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