RHF350 STMICROELECTRONICS [STMicroelectronics], RHF350 Datasheet - Page 13

• Manufacturer Part Number: RHF350
• Description: Rad-hard 550 MHz low noise operational amplifier
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

RHF350
4.1
4.2
4.3
Equation 4
The input noise of the instrumentation must be extracted from the measured noise value.
The real output noise value of the driver is:
Equation 5
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 6
Measurement of the input voltage noise eN
If we assume a short-circuit on the non-inverting input (R3 = 0), from
derive:
Equation 7
In order to easily extract the value of eN , the resistance R2 will be chosen to be 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 in order to decrease the thermal noise contribution.
Measurement of the positive input current noise iNp
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 = 100 W, gain: g = 10
2
eNo
=
eN
eNo
eNo
2
2
=
=
=
eN
g
2
2
+
eN
Equation 5
Measured
iNn
2
g
2
2
+
g
iNn
2
R2
+
iNn
2
, a resistance R3 is connected to the non-inverting input. The
Doc ID 15604 Rev 4
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 4
2
2
+
g
4kTR1
4kTR2
we obtain:
+
4kTR2
+
1
Noise measurements
Equation 6
+
R2
------- -
R1
+
Equation 7
1
2
+
R2
------- -
R1
4kTR3
2
we can
. This
4kTR3
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