OPA2690IDBV BURR-BROWN [Burr-Brown Corporation], OPA2690IDBV Datasheet - Page 14

• Manufacturer Part Number: OPA2690IDBV
• Description: Dual, Wideband, Voltage-Feedback OPERATIONAL AMPLIFIER with Disable
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

OPA2690
SBOS238D − JUNE 2002 − REVISED DECEMBER 2004
Again, an additional resistor (50Ω in this case) is included
directly in series with the noninverting input. This minimum
recommended value provides part of the DC source
resistance matching for the noninverting input bias
current. It is also used to form a simple parasitic pole to roll
off the frequency response at very high frequencies
( > 500MHz) using the input parasitic capacitance. The
gain resistor (R
gain of +1, which puts the input DC bias voltage (2.5V) on
the output as well. The output voltage can swing to within
1V of either supply pin while delivering > 100mA output
current. A demanding 100Ω load to a midpoint bias is used
in this characterization circuit. The new output stage circuit
used in the OPA2690 can deliver large bipolar output
currents into this midpoint load with minimal crossover
distortion, as shown in the +5V supply harmonic distortion
plots.
SINGLE-SUPPLY ADC INTERFACE
Most modern, high-performance ADCs (such as the TI
ADS8xx and ADS9xx series) operate on a single +5V (or
lower) power supply. It has been a considerable challenge
for single-supply op amps to deliver a low distortion input
signal at the ADC input for signal frequencies exceeding
5MHz. The high slew rate, exceptional output swing, and
high linearity of the OPA2690 make it an ideal
single-supply ADC driver. The circuit on the front page
shows one possible interface paricularly suited to
differential I/O, AC-coupled requirements. Figure 4 shows
the test circuit of Figure 2 modified for a capacitive (ADC)
load and with an optional output pull-down resistor (R
This circuit would be suitable to dual-channel ADC driving
with a single-ended I/O.
14
G
V
) is AC-coupled, giving the circuit a DC
I
1V
PP
59Ω
0.1µF
698Ω
698Ω
50Ω
Figure 4. SFDR versus I
402Ω
0.1 µ F
B
).
+5V
O P A 2 6 9 0
1 /2
402Ω
The OPA2690 in the circuit of Figure 4 provides > 200MHz
bandwidth for a 2V
distortion or 2-tone, 3rd-order intermodulation distortion
will be observed due to the very low crossover distortion
in the OPA2690 output stage. The limit of output
Spurious-Free Dynamic Range (SFDR) will be set by the
2nd-harmonic distortion. Without R
measured at 10MHz shows an SFDR of 57dBc. This can
be improved by pulling additional DC bias current (I
of the output stage through the optional R
ground (the output midpoint is at 2.5V for Figure 4).
Adjusting I
Figure 3. SFDR improvement is achieved for I
to 5mA, with worse performance for higher values. Using
the dual OPA2690 in an I/Q receiver channel will give
matched AC performance through high frequencies.
Power−supply decoupling not shown.
R
B
70
68
66
64
62
60
58
56
54
52
50
0
B
V
B
O
I
B
30Ω
= 2V
R
gives the improvement in SFDR shown in
1
S
Figure 3. SFDR versus I
PP
, 10MHz
2
PP
Output Pull−Down Current (mA)
output swing. Minimal 3rd-harmonic
3
50pF
4
5
2.5V DC
± 1V AC
ADC Input
B
6
, the circuit of Figure 4
7
B
8
www.ti.com
B
B
resistor to
values up
9
B
) out
10