Datasheet

OPA690
High-Speed
DAC
V =I R
O O F
R
F
C
F
C
D
I
O
I
O
50W
1
2 R Cp
F F
=
GBP
4 R Cp
F D
f =
-3dB
GBP
2 R Cp
DF
OPA690
2kW
0.1 Fm
400W50W
50W
+12V
5pF
1V
PP
50W
Source
8V
PP
4V
PP
50W
Load
2kW
OPA690
SBOS223F –DECEMBER 2001–REVISED FEBRUARY 2010 www.ti.com
HIGH-PERFORMANCE DAC The 5pF capacitor in the feedback loop provides
TRANSIMPEDANCE AMPLIFIER added bandwidth control for the signal path.
High-frequency, direct digital synthesis (DDS)
Digital-to-Analog Converters (DACs) require a low
distortion output amplifier to retain their SFDR
performance into real-world loads. See Figure 40 for
a single-ended output drive implementation. In this
circuit, only one side of the complementary output
drive signal is used. The diagram shows the signal
output current connected into the virtual ground
summing junction of the OPA690, which is set up as
a transimpedance stage or I-V converter. The unused
current output of the DAC is connected to ground. If
the DAC requires that its outputs terminate to a
compliance voltage other than ground for operation,
the appropriate voltage level may be applied to the
noninverting input of the OPA690. The dc gain for this
circuit is equal to R
F
. At high frequencies, the DAC
output capacitance will produce a zero in the noise
gain for the OPA690 that may cause peaking in the
closed-loop frequency response. C
F
is added across
R
F
to compensate for this noise gain peaking. To
Figure 40. DAC Transimpedance Amplifier
achieve a flat transimpedance frequency response,
the pole in the feedback network should be set to:
(1)
which will give a closed-loop transimpedance
bandwidth, f
−3dB
, of approximately:
(2)
Where GBP = gain bandwidth product (Hz) for the
OPA690.
HIGH-POWER LINE DRIVER
The large output swing capability of the OPA690 and
its high current capability allow it to drive a 50Ω line
Figure 41. High-Power Coax Line Driver
with a peak-to-peak signal up to 4V
PP
at the load, or
8V
PP
at the output of the amplifier using a single 12V
supply. Figure 41 shows such a circuit set for a gain
of 8 to the output or 4 to the load.
16 Copyright © 2001–2010, Texas Instruments Incorporated
Product Folder Link(s): OPA690