AD8335 datasheet(21/24 Pages) AD

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AD8335

Rev. 0 | Page 21 of 24

BASIC CONNECTIONS

Figure 58 shows the basic connections for the AD8335. Input

signals enter from the left and output signals exit from the right,

providing straight-line signal paths. Of course, a device with

four differential VGAs such as this requires a multilayer printed

circuit board. Power supply isolation is shown for the preamps,

and for the VGA sections. If components are mounted to both

sides of the board, those in the signal path should be located on

the top, with power-supply decoupling components on the

wiring side.

PREAMP CONNECTIONS

To configure the AD8335 for input matching a feedback resistor

(RFB) is ac-coupled between Pin PONx and Pin PIPx. AC coupling

accommodates dissimilar common-mode voltages at the input

and output ports. For values of RSOURCE between 50 Ω and 200 Ω,

RFB is simply 5 × RSOURCE. Table 6 lists a few larger values of source

resistor (or RIN), along with the exact value and nearest standard

1% feedback resistor. For values other those than listed in Table 6,

RFB can be calculated using Equation 5. For values larger than

1 kΩ, it may be advantageous to simply remove RFB.

Table 6. Feedback Resistor Values for Various Input Resistances

RIN (Ω)

Exact RFB Value (Ω)

Nearest Standard 1% Value (Ω)

200

1014

1.02k

500

2588

2.61k

1000

5365

5.36k

)

(

−

Ω

(5)

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