Datasheet AD8079 (Analog Devices) - 8
| Manufacturer | Analog Devices |
| Description | Dual 260 MHz Gain = +2.0 & +2.2 Buffer |
| Pages / Page | 12 / 8 — AD8079. CABLE. ( INTERNAL). VOUT #1. I BI. 4.7µF. RSERIES. I BN. VOUT. … |
| Revision | A |
| File Format / Size | PDF / 357 Kb |
| Document Language | English |
AD8079. CABLE. ( INTERNAL). VOUT #1. I BI. 4.7µF. RSERIES. I BN. VOUT. 0.1µF. 1/2. VOUT #2. Driving Capacitive Loads. VIN. –VS. VOUT #3. OUT #4
Model Line for this Datasheet
Text Version of Document
AD8079 R 75
Ω
F CABLE ( INTERNAL) 75
Ω
VOUT #1 RI I BI +V ( INTERNAL) S 4.7µF 75
Ω
RSERIES I BN VOUT 0.1µF RN CL 7 75
Ω
2 CABLE 75
Ω
1/2 8 VOUT #2 AD8079 1 0.1µF 6 75
Ω Figure 24. Output Offset Voltage
75
Ω
CABLE 4.7µF Driving Capacitive Loads VIN
The AD8079 was designed primarily to drive nonreactive loads.
75
Ω
–VS
If driving loads with a capacitive component is desired, best frequency response is obtained by the addition of a small series
75
Ω
4 CABLE
output resistance (RSERIES). The graph in Figure 25 shows the
1/2 75
Ω
5 VOUT #3
optimum value for R
AD8079
SERIES vs. capacitive load. It is worth noting
3
that the frequency response of the circuit when driving large
75
Ω capacitive loads will be dominated by the passive roll-off of
75
Ω R
CABLE
SERIES and CL.
75
Ω
V 40 OUT #4 75
Ω
30
Figure 26. Video Line Driver Ω
– Single-Ended to Differential Driver Using an AD8079 20
The two halves of an AD8079 can be configured to create a
SERIESR
single-ended to differential high speed driver with a –3 dB band- width in excess of 110 MHz as shown in Figure 27. Although
10
the individual op amps are each current feedback with internal feedback resistors, the overall architecture yields a circuit with attributes normally associated with voltage feedback amplifiers,
0
while offering the speed advantages inherent in current feedback
0 5 10 15 20 25 CL – pF
amplifiers. In addition, the gain of the circuit can be changed by varying a single resistor, RF, which is often not possible in a dual Figure 25. Recommended R op amp differential driver. SERIES vs. Capacitive Load
CC = 1.5pF Operation as a Video Line Driver
The AD8079 has been designed to offer outstanding perfor-
R R F 750
Ω mance as a video line driver. The important specifications of
G 750
Ω
OP AMP #1
differential gain (0.01%) and differential phase (0.02°) meet the
V 50
Ω
IN 1/2 OUTPUT #1
most exacting HDTV demands for driving one video load with
AD8079
each amplifier. The AD8079 also drives four back terminated loads (two each), as shown in Figure 26, with equally impressive performance (0.01%, 0.07°). Another important consideration is isolation between loads in a multiple load application. The AD8079 has more than 40 dB of isolation at 5 MHz when driv- ing two 75 Ω back terminated loads.
50
Ω
1/2 OUTPUT #2 AD8079 OP AMP #2
Figure 27. Differential Line Driver –8– REV. A
Ω
F CABLE ( INTERNAL) 75
Ω
VOUT #1 RI I BI +V ( INTERNAL) S 4.7µF 75
Ω
RSERIES I BN VOUT 0.1µF RN CL 7 75
Ω
2 CABLE 75
Ω
1/2 8 VOUT #2 AD8079 1 0.1µF 6 75
Ω Figure 24. Output Offset Voltage
75
Ω
CABLE 4.7µF Driving Capacitive Loads VIN
The AD8079 was designed primarily to drive nonreactive loads.
75
Ω
–VS
If driving loads with a capacitive component is desired, best frequency response is obtained by the addition of a small series
75
Ω
4 CABLE
output resistance (RSERIES). The graph in Figure 25 shows the
1/2 75
Ω
5 VOUT #3
optimum value for R
AD8079
SERIES vs. capacitive load. It is worth noting
3
that the frequency response of the circuit when driving large
75
Ω capacitive loads will be dominated by the passive roll-off of
75
Ω R
CABLE
SERIES and CL.
75
Ω
V 40 OUT #4 75
Ω
30
Figure 26. Video Line Driver Ω
– Single-Ended to Differential Driver Using an AD8079 20
The two halves of an AD8079 can be configured to create a
SERIESR
single-ended to differential high speed driver with a –3 dB band- width in excess of 110 MHz as shown in Figure 27. Although
10
the individual op amps are each current feedback with internal feedback resistors, the overall architecture yields a circuit with attributes normally associated with voltage feedback amplifiers,
0
while offering the speed advantages inherent in current feedback
0 5 10 15 20 25 CL – pF
amplifiers. In addition, the gain of the circuit can be changed by varying a single resistor, RF, which is often not possible in a dual Figure 25. Recommended R op amp differential driver. SERIES vs. Capacitive Load
CC = 1.5pF Operation as a Video Line Driver
The AD8079 has been designed to offer outstanding perfor-
R R F 750
Ω mance as a video line driver. The important specifications of
G 750
Ω
OP AMP #1
differential gain (0.01%) and differential phase (0.02°) meet the
V 50
Ω
IN 1/2 OUTPUT #1
most exacting HDTV demands for driving one video load with
AD8079
each amplifier. The AD8079 also drives four back terminated loads (two each), as shown in Figure 26, with equally impressive performance (0.01%, 0.07°). Another important consideration is isolation between loads in a multiple load application. The AD8079 has more than 40 dB of isolation at 5 MHz when driv- ing two 75 Ω back terminated loads.
50
Ω
1/2 OUTPUT #2 AD8079 OP AMP #2
Figure 27. Differential Line Driver –8– REV. A
