TSH350_07 STMICROELECTRONICS [STMicroelectronics], TSH350_07 Datasheet - Page 15

• Manufacturer Part Number: TSH350_07
• Description: 550MHz low noise current feedback amplifier
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

TSH350
Measurement of the input voltage noise eN
Measurement of the negative input current noise iNn
Measurement of the positive input current noise iNp
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 equivalent input noise because 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 4
If we assume a short-circuit on the non-inverting input (R3=0), from
derive:
Equation 5
In order to easily extract the value of eN, the resistance R2 will be chosen to be as low as
possible. In the other hand, the gain must be large enough:
To measure the negative input current noise iNn, we set R3=0 and use
time, the gain must be lower in order to decrease the thermal noise contribution:
To extract iNp from
value of R3 must be chosen in order to keep its thermal noise contribution as low as
possible against the iNp contribution:
eNo
R3=0, gain: g=100
R3=0, gain: g=10
R3=100W, gain: g=10
2
eNo
=
eN
eNo
eNo
2
2
=
=
=
eN
g
2
2
+
eN
Equation
Measured
iNn
2
g
2
2
+
g
iNn
2
R2
+
3, a resistance R3 is connected to the non-inverting input. The
iNn
2
2
2
+
–
2
R2
iNp
instrumentation
2
R2
2
+
iNp
2
R3
+
g
2
2
R3
4kTR2
g
2
2
+
R2
------- -
R1
2
g
Equation 2
2
2
+
g
4kTR1
4kTR2
we obtain:
+
4kTR2
+
Equation 4
1
Noise measurements
+
Equation
R2
------- -
R1
+
1
2
+
R2
------- -
R1
4kTR3
we can
2
5. This
4kTR3
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