clc428 National Semiconductor Corporation, clc428 Datasheet - Page 4

• Manufacturer Part Number: clc428
• Description: Dual Wideband, Low-noise, Voltage Feedback Op Amp
• Manufacturer: National Semiconductor Corporation

Low Noise Design
Ultimate low noise performance from circuit designs using
the CLC428 requires the proper selection of
external resistors. By selecting appropriate low-valued
resistors for R
can achieve output noise that is approximately the
equivalent voltage input noise of 2.0 nV/ Hz multiplied
by the desired gain (Av).
Each amplifier in the CLC428 has an equivalent
input noise resistance which is optimum for matching
source impedances of approximately 1k. Using a
transformer, any source can be matched to achieve the
lowest noise design.
For even lower noise performance than the CLC428,
consider the CLC425 or CLC426 at 1.05 and 1.6 nV/ Hz,
respectively.
DC Bias Currents and Offset Voltages
Cancellation of the output offset voltage due to input bias
currents is possible with the CLC428. This is done by
making the resistance seen from the inverting and non-
inverting inputs equal. Once done, the residual output
offset voltage will be the input offset voltage (Vos) multi-
plied by the desired gain (Av). Comlinear Application Note
OA-7 offers several solutions to further reduce the output
offset.
http://www.national.com
f
and R
g
, amplifier circuits using the CLC428
Application Discussion
4
Output and Supply Considerations
With ±5V supplies, the CLC428 is capable of a typical
output swing of ±3.8V
Additional output swing is possible with slightly higher
supply voltages. For loads of less than 50 , the output
swing will be limited by the CLC428’s output current
capability, typically 80mA.
Output settling time when driving capacitive loads can be
improved by the use of a series output resistor. See the
plot labeled "Settling Time vs. Capacitive Load" in the
Typical Performance section.
Layout
Proper power supply bypassing is critical to insure good high
frequency performance and low noise. De-coupling capaci-
tors of 0.1 F should be place as close as possible to the
power supply pins. The use of surface mounted capacitors
is recommended due to their low series inductance.
A good high frequency layout will keep power supply and
ground traces away from the inverting input and output
pins. Parasitic capacitance from these nodes to ground
causes frequency response peaking and possible circuit
oscillation. See OA-15 for more information. National
suggests the CLC730038 (through-hole) or the CLC730036
(SOIC) dual op amp evaluation board as a guide for high
frequency layout and as an aid in device evaluation.
under a no-load condition.