Datasheet

Data Sheet AD8335
Rev. B | Page 23 of 28
EVALUATION BOARD
The AD8335 evaluation board is a convenient way to experiment
with the operation and features of the AD8335 quad VGA.
Switches connect or disconnect the low noise preamp and VGA
channels and the two gain ranges. Just connect a 5 V/200 mA
power supply to the red and black test loop and a differential
probe (or two single-ended scope probes) to the output 2-pin
headers to observe the output voltage. Test loops are also provided
for the gain voltage inputs, which are typically dc bias voltages
between 0 V and 3 V. The LNA and VGA channels are enabled
independently. All channels are tested functionally before shipment.
The low noise preamp active input matching is configured for
50 Ω to terminate a corresponding signal generator or network
analyzer. Input impedances up to 14.7 kΩ are possible by
adjusting R
FB
1
through R
FB
4
using the resistor values listed in
Table 6. All passive components are 0603 size surface-mount
components. A low noise voltage source (be careful of noise at
the switching supply terminals) is recommended for gain control
voltage (VGN1, VGN2, VGN3, and VGN4) inputs.
BOARD LAYOUT
The evaluation board has a four-layer construction that provides a
solid near-zero impedance ground, with power and ground on
the inner layers, and interconnecting circuitry on the outer layers.
Figure 63 through Figure 68 illustrate various board layers.
04976-060
Figure 60. Photograph of the AD8335-EVALZ Evaluation Board