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DS51868A-page 11

Figure 1-3 shows the power supply circuitry. R

1

 and R

2

 provide high frequency isolation 

of the supply lines. They also help with series resonances in the supplies. C

1

 and C

2

 

provide the bulk bypassing, while C

3

 and C

4

 provide the local bypassing, for U

1

 

(MCP661).

The power supplies use surface mount test points to connect to the lab supplies. The 
signal input and output are connected via BNC recepticles (and coax cables) to 50

Ω 

lab equipment.

The PCB has two 50

Ω transmission lines between the BNC recepticles and the 

matching resistors (R

3

 and R

7

 in Figure 1-2). They are 100 mils (2.54 mm) wide, which 

is a value commonly used for standard FR4 PCBs with only two layers. These lines are 
as long as possible; they end at the matching resistors (to avoid parasitic capacitance 
issues).

V

DDX

(+2.5V)

GND

(0V)

V

SSX

(-2.5V)

R

1

1.0

Ω

R

2

1.0

Ω

C

1

C

2

10 µF

10 µF

U

1

C

3

100 nF

C

4

100 nF