參數(shù)資料
型號(hào)： OP634
廠商： Texas Instruments, Inc.
英文描述： Wideband, Single-Supply Operational Amplifier(寬帶,單電源運(yùn)算放大器)
中文描述： 寬帶，單電源運(yùn)算放大器（寬帶，單電源運(yùn)算放大器）
文件頁(yè)數(shù)： 17/18頁(yè)
文件大?。?/td> 284K
代理商： OP634
OPA634, OPA635
SBOS097A
17
c) Careful selection and placement of external compo-
nents will preserve the high-frequency performance.
Resistors should be a very low reactance type. Surface-
mount resistors work best and allow a tighter overall layout.
Metal film or carbon composition axially-leaded resistors
can also provide good high-frequency performance. Again,
keep their leads and PC board traces as short as possible.
Never use wirewound type resistors in a high-frequency
application. Since the output pin and inverting input pin are
the most sensitive to parasitic capacitance, always position
the feedback and series output resistor, if any, as close as
possible to the output pin. Other network components, such
as non-inverting input termination resistors, should also be
placed close to the package. Where double-side component
mounting is allowed, place the feedback resistor directly
under the package on the other side of the board between the
output and inverting input pins. Even with a low parasitic
capacitance shunting the external resistors, excessively high
resistor values can create significant time constants that can
degrade performance. Good axial metal film or surface-
mount resistors have approximately 0.2pF in shunt with the
resistor. For resistor values >1.5k
, this parasitic capaci-
tance can add a pole and/or zero below 500MHz that can
effect circuit operation. Keep resistor values as low as
possible consistent with load driving considerations. The
750
feedback used in the typical performance specifica-
tions is a good starting point for design
d) Connections to other wideband devices
on the board
may be made with short direct traces or through on-board
transmission lines. For short connections, consider the trace
and the input to the next device as a lumped capacitive load.
Relatively wide traces (50mils to 100mils) should be used,
preferably with ground and power planes opened up around
them. Estimate the total capacitive load and set R
S
from the
typical performance curve “Recommended R
S
vs Capacitive
Load”. Low parasitic capacitive loads (< 5pF) may not need
an R
S
since the OPA634 and OPA635 are nominally com-
pensated to operate with a 2pF parasitic load. Higher para-
sitic capacitive loads without an R
S
are allowed as the signal
gain increases (increasing the unloaded phase margin) If a
long trace is required, and the 6dB signal loss intrinsic to a
doubly-terminated transmission line is acceptable, imple-
ment a matched impedance transmission line using microstrip
or stripline techniques (consult an ECL design handbook for
microstrip and stripline layout techniques). A 50
environ-
ment is normally not necessary on board, and in fact, a
higher impedance environment will improve distortion as
shown in the distortion versus load plots. With a character-
istic board trace impedance defined (based on board material
and trace dimensions), a matching series resistor into the
trace from the output of the OPA634 and OPA635 is used as
well as a terminating shunt resistor at the input of the
destination device. Remember also that the terminating
impedance will be the parallel combination of the shunt
resistor and the input impedance of the destination device;
this total effective impedance should be set to match the
trace impedance. If the 6dB attenuation of a doubly termi-
nated transmission line is unacceptable, a long trace can be
series-terminated at the source end only. Treat the trace as a
capacitive load in this case and set the series resistor value
as shown in the typical performance curve “Recommended
R
S
vs Capacitive Load”. This will not preserve signal integ-
rity as well as a doubly-terminated line. If the input imped-
ance of the destination device is low, there will be some
signal attenuation due to the voltage divider formed by the
series output into the terminating impedance.
e) Socketing a high-speed part is not recommended.
The
additional lead length and pin-to-pin capacitance introduced
by the socket can create an extremely troublesome parasitic
network which can make it almost impossible to achieve a
smooth, stable frequency response. Best results are obtained
by soldering the OPA634 and OPA635 onto the board. If
socketing for the DIP package is desired, high frequency
flush mount pins (e.g., McKenzie Technology #710C) can
give good results.
INPUT AND ESD PROTECTION
The OPA634 and OPA635 are is built using a very high-
speed complementary bipolar process. The internal junction
breakdown voltages are relatively low for these very small
geometry devices. These breakdowns are reflected in the
Absolute Maximum Ratings table. All device pins are pro-
tected with internal ESD protection diodes to the power
supplies, as shown in Figure 8.
External
Pin
+V
CC
–
V
CC
Internal
Circuitry
FIGURE 8. Internal ESD Protection.
These diodes provide moderate protection to input overdrive
voltages above the supplies as well. The protection diodes
can typically support 30mA continuous current. Where higher
currents are possible (e.g., in systems with
±
15V supply
parts driving into the OPA634 and OPA635), current-limit-
ing series resistors should be added into the two inputs. Keep
these resistor values as low as possible, since high values
degrade both noise performance and frequency response.
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