Datasheet
Table Of Contents
- FEATURES
- APPLICATIONS
- DESCRIPTION
- ABSOLUTE MAXIMUM RATINGS
- ELECTRICAL CHARACTERISTICS: VS = ±5V
- TYPICAL CHARACTERISTICS: VS = ±5V
- APPLICATION INFORMATION
- WIDEBAND CURRENT FEEDBACK OPERATION
- ADC DRIVER
- WIDEBAND INVERTING SUMMING AMPLIFIER
- SAW FILTER BUFFER
- WIDEBAND UNITY GAIN BUFFER WITH IMPROVED FLATNESS
- DESIGN-IN TOOLS
- OPERATING SUGGESTIONS
- SETTING RESISTOR VALUES TO OPTIMIZE BANDWIDTH
- OUTPUT CURRENT AND VOLTAGE
- DRIVING CAPACITIVE LOADS
- DISTORTION PERFORMANCE
- NOISE PERFORMANCE
- DC ACCURACY AND OFFSET CONTROL
- THERMAL ANALYSIS
- BOARD LAYOUT GUIDELINES
- INPUT AND ESD PROTECTION
- REVISION HISTORY
- REVISION HISTORY
Single-to-Differential
Gainof10
Power-supplydecouplingnotshown.
OPA694
L
+5V
L
R
1
R
1
R
2
R
2
C
V-
V+
12-Bit
ADC
OPA694
500W
-5V
0.1 Fm
25W
100W
100W 500W
C
1
C
1
V
I
50W
1:2
25W
V
CM
100W
50W
OPA694
+5V
-5V
100MHz, 1dBCompression=15dBm-
50W
50W
50W
50W
50W
RG-58
50W
30W
V
1
V
2
V
3
V
4
V
5
V V V +V +V +V
O 1 2 3 4 5
= ( + )-
OPA694
www.ti.com
SBOS319G –SEPTEMBER 2004–REVISED JANUARY 2010
Two OPA694s are used in the circuit of Figure 33 to have been adjusted to maintain both maximum
form a differential driver for a 12-bit ADC. The two bandwidth and input impedance matching. If each R
F
OPA694s offer > 250MHz bandwidth at a differential signal is assumed to be driven from a 50Ω source,
gain of 5V/V, with a 2V
PP
output swing. A 2nd-order the NG for this circuit will be [1 + 100Ω/(100Ω/5)] = 6.
RLC filter is used in order to limit the noise from the The total feedback impedance (from V
O
to the
amplifier and provide some attenuation for inverting error current) is the sum of R
F
+ (R
I
• NG),
higher-frequency harmonic distortion. where R
I
is the impedance looking into the inverting
input from the summing junction (see the Setting
Resistor Values to Optimize Performance section).
WIDEBAND INVERTING SUMMING
Using 100Ω feedback (to get a signal gain of –2 from
AMPLIFIER
each input to the output pin) requires an additional
Since the signal bandwidth for a current-feedback op
30Ω in series with the inverting input to increase the
amp can be controlled independently of the noise
feedback impedance. With this resistor added to the
gain (NG, which is normally the same as the
typical internal R
I
= 30Ω, the total feedback
noninverting signal gain), wideband inverting
impedance is 100Ω + (60Ω • 6) = 460Ω, which is
summing stages may be implemented using the
equal to the required value to get a maximum
OPA694. The circuit in Figure 34 shows an example
bandwidth flat frequency response for NG = 6.
inverting summing amplifier, where the resistor values
Figure 33. Wideband, AC-Coupled, Low-Power ADC Driver
Figure 34. 200MHz RF Summing Amplifier
Copyright © 2004–2010, Texas Instruments Incorporated 11
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