3 Components
4 Board Layout
5 Measurement Tips
Components
Components that have RF performance similar to the ones listed in Table 1 may be substituted. C
1
and C
2need a larger voltage rating for ±15V dual supplies.
Table 1. Component Descriptions
PART DESCRIPTION
C
1
, C
2
Tantalum Chip Capacitor, SMD EIA Size 3528, 20VC
3
, C
4
Multilayer Ceramic Chip Capacitor, SMD 0603, 50VC
5
Multilayer Ceramic Chip Capacitor, SMD 0805, 50VIN_A, IN_B, SMA or SMB Board Jack (Amphenol 901-144-8)IN_C, OUT_A,
OUT_B,
OUT_C, Dis_A,Dis_B, Dis_C
EMI-Suppression Ferrite Chip, SMD 0805L
1
, L
2
(Steward LI 0805 B 900 R)Terminal Block, 3.5mm CentersTB
1
(On-Shore Technology ED555/3DS)
R
1
through R
3
and R
10
through R
18
set the I/O impedance, R
4
through R
9
set the gain, and C
1
through C
5are supply bypass capacitors. C
5
is optional; it adds a bypass between the supplies that improvesdistortion performance for some models. L
1
and L
2
are ferrite chips that can reduce interactions with thepower supply at high frequencies. If not desired, they can be replaced with 0 Ωresistors.
This demonstration fixture is a two-layer PCB. (See Figure 3 .) It uses a ground plane on the bottom, andsignal and power traces on the top. The ground plane has been opened up around op amp pins sensitiveto 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-frequencyamplifiers. The tantalum capacitors, C
1
and C
2
, do not need to be as close to pins 7 and 4 on the PCB,and may be shared with other amplifiers.
See the individual op amp data sheet for more information on proper board layout techniques andcomponent selection.
This demonstration fixture, with the component values shown, is designed to operate in a 50 Ωenvironment; most data sheet plots are obtained under these conditions. It is easy to change thecomponent values for different input and output impedance levels. However, do not use high-impedanceprobes; they represent a heavy capacitive load to the op amp, and will alter the amplifier response.Instead, use low-impedance ( ≤500 Ω) probes with adequate bandwidth. The probe input capacitance andresistance set an upper limit on the measurement bandwidth. If a high-impedance probe must be used,place a 100 Ωresistor on the probe tip to isolate its capacitance from the circuit.
SBOU046 – April 2007 DEM-OPA-SSOP-3D Demonstration Fixture 3Submit Documentation Feedback