RF2721 datasheet(4/6 Pages) RFMD

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Preliminary

2-30

RF2721

Rev A2 010509

Function

Description

Interface Schematic

I OUT

Demodulated baseband I output. The reference DC level of this pin is

set by the voltage of pin 9 (REF IN), which is connected to this pin

through a 5k

Ω resistor to the collectors of this push-pull output. This

results in an output impedance of 5k

Ω if the REF IN pin is connected to

a low impedance source. The capacitance of the load determines the

maximum baseband frequency. A very low capacitive load may stretch

the 3dB bandwidth over 10MHz. Another way to increase bandwidth is

by connecting a shunt resistor. This will trade gain for bandwidth.

See pin 8.

GND

Same as pin 2.

Power down control. When this pin is "low", all circuits are shut off. A

"low" is typically 0.8V or less at room temperature. When this pin is

"high", all circuits are operating normally.

VCC

Power supply pin. An external 100nF bypass capacitor is recom-

mended if no other bypass capacitor is nearby.

IF IN-

Balanced IF input. An input level of 400mVPP gives full output swing; a

level of maximum 250mVPP is recommended for linear operation. This

pin has no internal DC block and an external capacitor of 100nF is

needed if connected to a DC path. If the IF is driven by a single-ended

source, connect this pin to an 100nF capacitor to ground.

See pin 1.

VCC

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