AD8610ARM Analog Devices, AD8610ARM Datasheet - Page 15

• Manufacturer Part Number: AD8610ARM
• Description: Precision Very Low Noise Low Input Bias Current Wide Bandwith JFET Operational Amplifier
• Manufacturer: Analog Devices

High-Speed Filters
The four most popular configurations are Butterworth, Elliptical,
Bessel, and Chebyshev. Each type has a response that is optimized
for a given characteristic as shown in Table II.
In active filter applications using operational amplifiers, the
dc accuracy of the amplifier is critical to optimal filter performance.
The amplifier’s offset voltage and bias current contribute to output
error. Input offset voltage is passed by the filter, and may be
V
V
IN1
IN2
RG
Type
Butterworth
Chebyshev
Elliptical
Bessel (Thompson)
R4 2k
2k
AD8610
R1 1k
R7
AD8610
R2 1k
10pF
10pF
R8 2k
C2
C5
U1
U2
V+
V–
V+
V–
C4
15pF
Sensitivity
Moderate
Good
Best
Poor
R5 2k
15pF
AD8610
C3
U3
V–
V+
Table II. Filter Types
Overshoot
Good
Moderate
Poor
Best
R6
2k
V
OUT
amplified to produce excessive output offset. For low-frequency
applications requiring large value input resistors, bias and offset
currents flowing through these resistors will also generate an
offset voltage.
At higher frequencies, an amplifier’s dynamic response must be
carefully considered. In this case, slew rate, bandwidth, and open-
loop gain play a major role in amplifier selection. The slew rate
must be both fast and symmetrical to minimize distortion. The
amplifier’s bandwidth, in conjunction with the filter’s gain, will
dictate the frequency response of the filter. The use of a high perfor-
mance amplifier such as the AD8610 will minimize both dc and ac
errors in all active filter applications.
Second Order Low-Pass Filter
Figure 27 shows the AD8610 configured as a second order
Butterworth low-pass filter. With the values as shown, the corner
frequency of the filter will be 1 MHz. The wide bandwidth of
the AD8610 allows a corner frequency up to tens of megahertz.
The following equations can be used for component selection:
where C1 and C2 are in farads.
C
C
R
1
1
2
V
IN
=
=
=
Phase
Nonlinear
Linear
R
( )(
10k
( )(
2
R2
2
2
π
π
=
User Selected Typical Values
f
1 414
f
CUTOFF
0 707
CUTOFF
.
.
10k
R1
11pF
)( )
C2
)( )
R
R
1
1
(
Amplitude (Pass Band)
Max Flat
Equal Ripple
Equal Ripple
22pF
C1
AD8610
+13V
–13V
U1
5
:
10
k
AD8610
Ω
−
100
V
OUT
k
Ω
)