2
DEM-OPA268xN
OPA2680N
—Table III shows typical values for this part.
For more information, consult the data sheet.
DUAL SUPPLY
(G = +2)
DUAL SUPPLY
(G = –1)
SINGLE SUPPLY
(G = +1)
COMPONENT
R
4
R
5
R
6
Open
0
Open
0
Open
Open
Open
Open
Open
TABLE V. OPA2682N Changes.
(a)
(b)
FIGURE 3. DEM-OPA268xN Demonstration Board Layout; (a) Component Side Silkscreen and Metal, (b) Ground Plane Side
Silkscreen and Metal (bottom view).
DUAL SUPPLY
(G = +2)
DUAL SUPPLY
(G = –1)
SINGLE SUPPLY
(G = +1)
COMPONENT
R
1
R
2
R
3
R
4
R
5
R
6
R
7
49.9
178
Open
Open
402
402
49.9
2.2
μ
F
0.01
μ
F
0.1
μ
F
57.6
Open
210
402
Open
402
49.9
2.2
μ
F
0.01
μ
F
0.1
μ
F
49.9
0
Open
Open
Open
24.9
49.9
2.2
μ
F
Open
0.1
μ
F
C
1
, C
2
C
3
C
4
, C
5
NOTE: The I/O impedances are 50
.
TABLE III. OPA2680N.
OPA2681N
—Table IV shows typical values for this part.
To select component values for your op amp (especially R
6
),
consult its data sheet.
DUAL SUPPLY
(G = +2)
DUAL SUPPLY
(G = –1)
SINGLE SUPPLY
(G = +1)
COMPONENT
R
1
R
2
R
3
R
4
R
5
R
6
R
7
49.9
10.0
Open
Open
402
402
49.9
2.2
μ
F
0.01
μ
F
0.1
μ
F
57.6
Open
10.0
402
Open
402
49.9
2.2
μ
F
0.01
μ
F
0.1
μ
F
49.9
10.0
Open
Open
Open
402
49.9
2.2
μ
F
Open
0.1
μ
F
C
1
, C
2
C
3
C
4
, C
5
NOTE: The I/O impedances are 50
.
TABLE IV. OPA2681N.
OPA2682N
—The OPA2682N uses internal resistors to set
the gain at +1, +2 or –1. Use Table IV for the components,
except for the changes in Table V.
BOARD LAYOUT
This demonstration board is a two-layer PCB. It uses a
ground plane on the bottom and signal and power traces on
the top. The ground plane has been opened up around op
amp pins sensitive to capacitive loading. Power supply
traces are laid out to keep current loop areas to a minimum.
The SMA (or SMB) connectors may be mounted either
vertically or horizontally.
The location and type of capacitors used for power-supply
bypassing are crucial to high frequency amplifiers. The
tantalum capacitors, C
1
and C
2
, do not need to be as close to
pins 11 and 4 on your PCB and may be shared with other
amplifiers.
See the individual op amp data sheet for more information on
proper board layout techniques, and component selection.
MEASUREMENT TIPS
This demonstration board, and the component values shown,
are designed to operate in a 50
environment. Most data
sheet plots are obtained this way. It is easy to change the
component values for different input and output impedance
levels.
Do not use high impedance probes; they represent a heavy
capacitive load to the op amps, and will alter their response.
Instead, use low impedance (
≤
500
) probes with adequate
bandwidth. The probe input capacitance and resistance set
an upper limit on the measurement bandwidth. If a high
impedance probe must be used, place a 100
resistor on the
probe tip to isolate its capacitance from the circuit.