OPA3680 Datasheet, PDF (14/22 Pages) Burr-Brown (TI) – Triple, Wideband, Voltage-Feedback OPERATIONAL AMPLIFIER With Disable

R
Q_PR
R/δ
C
R
R
R
C
V_IN
V_OUT
49.9Ω
1/3
OPA3680
1/3
OPA3680
1/3
OPA3680
Q_PR/χ
Q_PR/β
αC
R_ISO
49.9Ω
49.9Ω
FIGURE 8. State Variable Filter.
STATE VARIABLE FILTER
Figure 8 shows a state variable filter using the OPA3680.
This active filter is quite useful for high Q filter responses,
and will produce lowpass, highpass, bandpass, notch and
allpass functions. The filter response is:
V_OUT
V_IN
=
–
s² (α) +
sω _P
Q_P
(β –
χ) +
ω
2
P
(δ)
s²
+
sω _P
Q_P
+
ω
2
P
(2)
ω_P
=
1
RC
The desired filter frequency response is achieved by the
correct selection of the feed-forward components at the
input.
The resistor R_ISO isolates the last op amp and the input
driver from capacitive loading problems when α > 0. To
ensure good performance, make sure that:
ω_P
2π
≤
 ^f_GBP


20Q
P
 ^fGBP
 20
,
,
Q_P >1
Q_P ≤ 1
(3)
where, f_GBP is the OPA3680’s gain bandwidth product
(300MHz).
DESIGN-IN TOOLS
DEMONSTRATION BOARDS
PC boards are available to assist in the initial evaluation of
circuit performance using the OPA3680. They are available
free as an unpopulated PC board delivered with descriptive
documentation. The summary information for the boards is
shown below:
PRODUCT
OPA3680E
OPA3680U
PACKAGE
16-Lead SSOP
SO-16
BOARD
PART
NUMBER
DEM-OPA368xE
DEM-OPA368xU
LITERATURE
REQUEST
NUMBER
MKT-354
MKT-364
Contact the Burr-Brown Applications support line
(1-800-548-6132) to request this board (ask for the desired
literature number).
MACROMODELS
Computer simulation of circuit performance using SPICE is
often useful when analyzing the performance of analog
circuits and systems. This is particularly true for Video and
RF amplifier circuits where parasitic capacitance and induc-
tance can have a major effect on circuit performance. A
SPICE model for the OPA680 is available through either the
Burr-Brown Internet web page (http://www.burr-brown.com).
These models do a good job of predicting small-signal AC
and transient performance under a wide variety of operating
conditions. They do not do as well in predicting the har-
monic distortion, temperature performance or dG/dφ charac-
teristics. These models do not attempt to distinguish be-
tween the package types in their small-signal AC perfor-
mance.
®
OPA3680
14