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CLC425A8B Datasheet(PDF) 7 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
Part No. CLC425A8B
Description  Ultra Low Noise Wideband Op Amp
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Maker  NSC [National Semiconductor (TI)]
Homepage  http://www.national.com
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CLC425A8B Datasheet(HTML) 7 Page - National Semiconductor (TI)

   
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Inverting Gains Less Than 10V/V
The lag compensation of Figure 9 will achieve stability
for lower gains. Placing the network between the two
input terminals does not affect the closed-loop nor noise
gain, but is best used for the invering configuration
because of its affect on the non-inverting input imped-
ance.
Single-Supply Operation
The CLC425 can be operated with single power supply
as shown iin Figure 10. Both the input and output are
capacitively coupled to set the dc operating point.
Low Noise Transimpedance Amplifier
The circuit of Figure 11 implements a low-noise transim-
pedance amplifier commonly used with photo-diodes.
The transimpedance gain is set by Rf. The simulated
frequency response is shown in Figure 12 and shows
the influence Cf has over gain flatness. Equation 4
provides the total input current noise density (ini) equa-
tion for the basic transimpedance configuration and is
plotted against feedback resistance (Rf) showing all
contributing noise sources in Figure 13. This plot indi-
cates the expected total equivalent input current noise
density (ini) for a given feedback resistance (Rf). The total
equivalent output voltage noise density (eno) is ini
∗R
f.
Very Low Noise Figure Amplifier
The circuit of Figure 14 implements a very low Noise
Figure amplifier using a step-up transformer combined
with a CLC425 and a CLC404. The circuit is configured
with a gain of 35.6dB. The circuit achieves measured
Noise Figures of less than 2.5dB in the 10-40MHz
region. 3rd order intercepts exceed +30dBm for frequen-
cies less than 40MHz and gain flatness of 0.5dB is measured
in the 1-50MHz pass bands. Application Note OA-14 provides
greater detail on these low Noise Figure techniques.
Rf
Rb
CLC425
+Vcc
Cf
Figure 11: Transimpedance Amplifier Configuration
AI
R
vin
f
=− ∗
Rf = 124
Rs = 75
Rg = 124
CLC425
Rin
Cin
39pF
Cf = 10pF
Icc=5mA
75
75
75
Figure 8: External Shunt Compensation
Figure 12: Transimpedance Amplifier Frequency Response
Rg
Rf
Rb
RL
CLC425
R
Vout
Rout
Vin
C
7
http://www.national.com
Figure 9: External Lag Compensation
Rf
R
RL
Rout
C
C
C
R
Rg
Vac
Vcc
Vcc
CLC425
Vcc
2
Vcc
2
+ AvVac
Vout =
Figure 10: Single Supply Operation
Equation 4: Total Equivalent Input Refered Current
ii
ni
n
n
ff
e
R
kT
R
=+
+


2
2
4
Figure 13: Current Noise Density vs. Feedback Resistance


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