RHF330 STMICROELECTRONICS [STMicroelectronics], RHF330 Datasheet - Page 15

• Manufacturer Part Number: RHF330
• Description: Rad-hard 1 GHz low noise operational amplifier
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

RHF330
5.1
5.2
5.3
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
Measurement of the input voltage noise eN
If we assume a short-circuit on the non-inverting input (R3=0), from
derive:
Equation 5
To easily extract the value of eN, the resistance R2 is as low as possible. On the other hand,
the gain must be large enough.
Measurement of the negative input current noise iNn
To measure the negative input current noise iNn, we set R3=0 and use
time, the gain must be lower to decrease the thermal noise contribution.
Measurement of the positive input current noise iNp
To extract iNp from
value of R3 must be chosen so that its thermal noise contribution is as low as possible
against the iNp contribution.
eNo
R3=0, gain: g=100
R3=0, gain: g=10
R3=100 W, gain: g=10
2
eNo
=
eN
2
2
=
eN
g
2
2
+
Equation
iNn
g
2
2
+
eNo
eNo
iNn
R2
3, a resistance R3 is connected to the non-inverting input. The
=
2
=
Doc ID 15576 Rev 3
2
+
R2
iNp
eN
Measured
2
2
2
+
iNp
g
R3
2
+
2
2
iNn
2
R3
g
–
2
2
2
instrumentation
+
R2
------- -
R1
R2
Equation 2
g
2
2
2
+
+
g
g
4kTR1
4kTR2
4kTR2
we obtain:
+
4kTR2
2
+
Equation 4
1
Noise measurements
+
Equation
R2
------- -
R1
+
1
2
+
R2
------- -
R1
4kTR3
we can
2
5. This
4kTR3
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