AD8260ACPZ-R7 datasheet(27/32 Pages) AD

27 / 32 page

AD8260

Rev. 0 | Page 27 of 32

CONNECTING THE EVALUATION BOARD

Figure 69 shows an evaluation board with typical test connec-

tions. The various pieces of test equipment are representative,

and equivalent equipment may be substituted.

The AD8260 includes two amplifier channels: a high current

driver and a digitally controlled VGA that is independently

enabled. The slide switch labeled ENABLE functions as the chip

enable, the GNSx switches permit the preamplifier/VGA to

operate, and the TX_EN switch enables the high current driver.

These independent enable functions permit the device to

operate in a send or listen mode when used as a transceiver.

The high current driver features differential inputs and is

optimally driven by a differential signal source. The input signal

is monitored at the 2-pin header labeled INP, using a differential

probe such as the Tektronix P6247 (not shown). Two 49.9 Ω

resistors are provided (R12 and R13), either for terminating

coaxial cables from a signal generator or to be used as load

resistors for a DAC with a current source output. An optional

external load resistor is connected at the SMA connector TXOP

and the output signal monitored at the 2-pin header labeled

TXOP_1.

As shipped, the gain of the high current driver is 1.5×, its default

value. The internal differential network with resistor values of

1 kΩ and 1.5 kΩ establishes this value. Other values of gain are

realized by connecting external resistors to the device at Pin 23,

Pin 24, Pin 27, Pin 28, and Pin 31, as shown in Figure 68, which

shows the internal structure for the default gain and how the

gain can be modified.

CCOMP

INPP

INRP

VOCM

TXFB

INRN

INPN

TXOP

VMDO

1kΩ

1.5kΩ

DEFAULT GAIN SETTING

COMPONENTS ARE SHOWN IN BLACK,

OPTIONAL COMPONENTS

ARE SHOWN IN GRAY.

1.5kΩ

–

Figure 68. Gain-Setting Resistors of the High Current Driver

The VGA/preamplifier is completely independent of the high

current driver and features a single-ended input at the SMA

connector PRAI. The input signal is monitored at the header

VPRE_IN. The output is monitored at the 2-pin header

VGA_OUT.

The gain bits, GNS0 through GNS3, must be set before the

VGA/preamplifier can operate. Table 4 lists the binary gain

codes. The board is shipped with both enables (ENBL and

TXEN) engaged and the gain-code switches adjusted for

maximum DGA gain (1011). Resistor R5 and Resistor R6

establish the preamplifier gain and are 100 Ω as shipped for a

noninverting preamplifier gain of 2×.

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