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CLC425A8B Schematic ( PDF Datasheet ) - National Semiconductor

Teilenummer CLC425A8B
Beschreibung Ultra Low Noise Wideband Op Amp
Hersteller National Semiconductor
Logo National Semiconductor Logo 




Gesamt 9 Seiten
CLC425A8B Datasheet, Funktion
N
CLC425
Ultra Low Noise Wideband Op Amp
June 1999
General Description
The CLC425 combines a wide bandwidth (1.9GHz GBW) with very
low input noise (1.05nV/Hz, 1.6pA/Hz) and low dc errors (100µV
VOS, 2µV/°C drift) to provide a very precise, wide dynamic-range
op amp offering closed-loop gains of 10.
Singularly suited for very wideband high-gain operation, the CLC425
employs a traditional voltage-feedback topology providing all the
benefits of balanced inputs, such as low offsets and drifts, as well
as a 96dB open-loop gain, a 100dB CMRR and a 95dB PSRR.
The CLC425 also offers great flexibility with its externally adjustable
supply current, allowing designers to easily choose the optimum
set of power, bandwidth, noise and distortion performance.
Operating from ±5V power supplies, the CLC425 defaults to a
15mA quiescent current, or by adding one external resistor, the
supply current can be adjusted to less than 5mA.
The CLC425's combination of ultra-low noise, wide gain-band-
width, high slew rate and low dc errors will enable applications in
areas such as medical diagnostic ultrasound, magnetic tape & disk
storage, communications and opto-electronics to achieve maximum
high-frequency signal-to-noise ratios.
The CLC425 is available in the following versions:
CLC425AJP
CLC425AJE
CLC425A8B
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
CLC425ALC -40°C to +85°C
CLC425AMC -55°C to +125°C
CLC425AJM5 -40°C to +85°C
DESC SMD number : 5962-93259.
8-pin PDIP
8-pin SOIC
8-pin CERDIP,
MIL-STD-883, Level B
dice
dice, MIL-STD-883, Level B
5-pin SOT
Features
s 1.9GHz gain-bandwidth product
s 1.05nV/Hz input voltage noise
s 0.8pA/Hz @ Icc < 5mA
s 100µV input offset voltage, 2µV/°C drift
s 350V/µs slew rate
s 15mA to 5mA adjustable supply current
s Gain range ±10 to ±1,000V/V
s Evaluation boards & simulation
macromodel
s 0.9dB NF @ Rs = 700
Applications
s Instrumentation sense amplifiers
s Ultrasound pre-amps
s Magnetic tape & disk pre-amps
s Photo-diode transimpedance amplifiers
s Wide band active filters
s Low noise figure RF amplifiers
s Professional audio systems
s Low-noise loop filters for PLLs
Equivalent Input Voltage Noise
10
1.05nV/Hz
1
100 1k 10k 100k 1M 10M 100M
Frequency (Hz)
Vo
VEE
Vnon-inv
Pinout
SOT23-5
VCC
Vinv
© 1999 National Semiconductor Corporation
Printed in the U.S.A.
Pinout
DIP & SOIC
NC 1
Vinv 2
Vnon-inv 3
-Vcc 4
-
+
8 Rp (optional)
7 +Vcc
6 Vout
5 NC
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CLC425A8B Datasheet, Funktion
As seen in Figure 5, eni is dominated by the intrinsic
voltage noise (en) of the amplifier for equivalent source
resistances below 33.5. Between 33.5and 6.43k,
eni is dominated by the thermal noise (et = 4kTR seq) of
the external resistors. Above 6.43k, eni is dominated by
the amplifier's current noise ( 2inRseq ). The point at
which the CLC425's voltage noise and current noise
contribute equally occurs for Rseq=464(i.e. en / 2in ).
As an example, configured with a gain of +20V/V giving
a -3dB of 90MHz and driven from an Rseq=25, the
CLC425 produces a total equivalent input noise voltage
(eni1.5790MHz ) of 16.5µVrms.
The noise figure is related to the equivalent source
resistance (Rseq) and the parallel combination of Rf and
Rg. To minimize noise figure, the following steps are
recommended:
Minimize Rf||Rg
Choose the optimum Rs (ROPT)
ROPT is the point at which the NF curve reaches a
minimum and is approximated by:
ROPT (en/in)
Figure 6 is a plot of NF vs Rs with Rf||Rg = 9.09 (Av = +10).
The NF curves for both Unterminated and Terminated
systems are shown. The Terminated curve assumes Rs
= RT. The table indicates the NF for various source
resistances including Rs = ROPT.
Figure 5: Voltage Noise Density vs. Source Resistance
If bias current cancellation is not a requirement, then
Rf||Rg does not need to equal Rseq. In this case, according
to Equation 1, Rf||Rg should be as low as possible in
order to minimize noise. Results similar to Equation 1
are obtained for the inverting configuration of Figure 2 if
Rseq is replaced by Rb and Rg is replaced by Rg+Rs. With
these substitutions, Equation 1 will yield an eni refered to
the non-inverting input. Refering eni to the inverting input
is easily accomplished by multiplying eni by the ratio of
non-inverting to inverting gains.
Noise Figure
Noise Figure (NF) is a measure of the noise degradation
caused by an amplifier.
Figure 6: Noise Figure vs Source Resistance
Supply Current Adjustment
The CLC425's supply current can be externally adjusted
downward from its nominal value by adding an optional
resistor (Rp) between pin 8 and the negative supply as
shown in Figure 7. Several of the plots found within the plot
pages demonstrate the CLC425’s behavior at different
supply currents. The plot labeled “Icc vs. Rp” provides the
means for selecting Rp and shows the result of standard IC
process variation which is bounded by the 25°C curve.
+Vcc
NF
=
10LOG

Si
So
/
/
Ni
No

=
10LOG

eni 2
et 2

The Noise Figure formula is shown in Equation 3. The
addition of a terminating resistor RT, reduces the
external thermal noise but increases the resulting NF.
The NF is increased because RT reduces the input signal
amplitude thus reducing the input SNR.
( ) ( )NF
=
10LOG
en 2
+
in
2
Rseq
+

Rf | | Rg
2
+ 4kTRseq
+ 4kT
4kTRseq
Rf | | Rg

Rseq = Rs for Unterminated Systems
Rseq = Rs II RT for Terminated Systems
Equation 3: Noise Figure Equation
37
CLC425 6
28
4
Rp
Vout
-Vcc
Figure 7: External Supply Current Adjustment
Non-Inverting Gains Less Than 10V/V
Using the CLC425 at lower non-inverting gains requires
external compensation such as the shunt compensation
as shown in Figure 8. The quiescent supply current must
also be reduced to 5mA with Rp for stability. The com-
pensation capacitors are chosen to reduce frequency
response peaking to less than 1dB. The plot in the
"Typical Performance" section labeled “Differential Gain
and Phase” shows the video performance of the CLC425
with this compensation circuitry.
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