AD9621 National Semiconductor Corporation, AD9621 Datasheet - Page 8

• Manufacturer Part Number: AD9621
• Description: CLC420 - High Speed, Voltage Feedback op Amp, Package: Lcc, Pin Nb=20
• Manufacturer: National Semiconductor Corporation

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Application Division
Description
The CLC420 is a high speed, slew boosted, voltage feed-
back amplifier with unity-gain stability. These features along
with matched inputs, low input bias and noise currents, and
excellent CMRR render the CLC420 very attractive for active
filters, differential amplifiers, log amplifiers, and transimped-
ance amplifiers.
DC accuracy
Unlike current feedback amplifiers, voltage-feedback ampli-
fiers have matched inputs. This means that the non inverting
and inverting input bias current are well matched and track
over temperature, etc. As a result, by matching the resis-
tance looking out of the two inputs, these errors can be
reduced to a small offset current term.
Gain bandwidth product
Since the CLC420 is a voltage feedback op amp, closed loop
bandwidth is approximately equal to the gain bandwidth
product (typically 100MHz) divided by the noise gain of the
circuit (for noise gains greater than 5). At lower noise gains,
higher order amplifier poles contribute to higher closed loop
bandwidth. At low gains use the frequency response perfor-
mance plots given in the data sheet.
FIGURE 1. Recommended Non-Inverting Gain Circuit
FIGURE 2. Recommended Inverting Gain Circuit
8
Another point to remember is that the closed loop bandwidth
is determined by the noise gain, not the signal gain of the
circuit. Noise gain is the reciprocal of the attenuation in the
feedback network enclosing the op amp. For example, a
CLC420 setup as a non-inverting amplifier with a closed loop
gain of +1 (a noise gain of 1) has a 300MHz bandwidth.
When used as an inverting amplifier with a gain of −1 (a
noise gain of 2), the bandwidth is less, typically only
100MHz.
Full-power bandwidth, and slew-rate
The CLC420 combines exceptional full power bandwidths
(40MHz, V
= +1) with low (40mW) power consumption. These attractive
results are achieved by using slew boosting circuitry to keep
the slew rates high while consuming very little power.
In non slew boosted amplifiers, full power bandwidth can be
easily determined from slew rate measurements, but in slew
boosting amplifiers, such as the CLC420, you can’t. For this
reason we provide data for both.
Slew rate is also different for inverting and non-inverting
configurations. This occurs because common-mode signal
voltages are present in non-inverting circuits but absent in
inverting circuits. Once again data is provided for both.
0
= 5Vpp, A
DS012752-17
DS012752-16
V
= +1) and slew rates (1100V/µs, A
V