RF2418PCBA Ver la hoja de datos (PDF) - RF Micro Devices

Número de pieza

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Fabricante

RF2418PCBA

LOW CURRENT LNA/MIXER

RF Micro Devices 

RF2418

Pin Function Description

Interface Schematic

1

LNA IN A series 10nH matching inductor is necessary to achieve specified gain

and noise figure at 900MHz. This pin is NOT internally DC-blocked. An

external blocking capacitor must be provided if the pin is connected to a

device with DC present. A DC path to ground (i.e. an inductor or resis-

tor to ground) is, however, acceptable at this pin. If a blocking capacitor

is required, a value of 22pF is recommended.

LNA IN

2

GND

Ground connection. Keep traces physically short and connect immedi-

ately to ground plane for best performance.

3

VDD1

Supply Voltage for the LNA only. A 22pF external bypass capacitor is

required and an additional 0.01μF is required if no other low frequency

bypass capacitors are near by. The trace length between the pin and

the bypass capacitors should be minimized. The ground side of the

bypass capacitors should connect immediately to ground plane.

For large input signals, VDD1 may be disconnected, resulting in the

LNA’s gain changing from +11dB to -26dB and current drain decreas-

ing by 4mA. If the LNA is never required for use, then this pin can be

left unconnected or grounded, and Pin 11 is used as the first input.

4

VDD2

Power supply for the IF buffer amplifier. If the high impedance mixer

output is being used, then this pin is not connected.

5

IF BYP

If this pin is connected to ground, an internal 10pF capacitor is con-

nected in parallel with the mixer output. This capacitor functions as an

LO trap, which reduces the amount of LO to IF bleed-through and pre-

vents high LO voltages at the mixer output from degrading the mixer’s

dynamic range. At higher IF frequencies, this capacitance, along with

parasitic layout capacitance, should be parallel resonated out by the

choice of the bias inductor value at pin 7. If the internal capacitor is not

connected to ground, the buffer amplifier could become unstable. A

~10pF capacitor should be added at the output to maintain the buffer’s

stability, but the gain will not be significantly affected.

6

IF2 OUT 50Ω buffered (open source) output port, one of two output options. Pin

7 must have a bias resistor to VDD and pin 6 must have a bias resistor

to ground (see Buffered Output Application Schematic) in order to turn

the buffer amplifier on. Current drain will increase by approximately

8mA at 5V, and by approximately 5mA at 3V. It is recommended that

these bias resistors be less than 1kΩ.

7

IF1 OUT High impedance (open drain) output port, one of two output options.

This pin must be connected to VDD through a resistor or inductor in

order to bias the mixer, even when using IF2 Output. In addition, a

0.01μF bypass capacitor is required at the other end of the bias resistor

or inductor. The ground side of the bypass capacitor should connect

immediately to ground plane. This output is intended to drive high

impedance IF filters. The recommended matching network is shunt L,

series C (see the application schematic, high impedance output). This

topology will provide matching, bias, and DC-blocking.

8

LO IN

Mixer LO input. A high-pass matching network, such as a single shunt

inductor (as shown in the application schematics), is the recommended

topology because it also rejects IF noise at the mixer input. This filtering

LO IN

is required to achieve the specified noise figures. This pin is NOT inter-

nally DC-blocked. An external blocking capacitor must be provided if

the pin is connected to a device with DC present. A DC path to ground

(i.e. an inductor or resistor to ground) is, however, acceptable at this

pin. If a blocking capacitor is required, a value of 22pF is recom-

mended.

9

RF BYP Connection for the external bypass capacitor for the mixer RF input

preamp. 1000pF is recommended. The trace length between the pin

and the capacitor should be minimized. The ground side of the bypass

capacitor should connect immediately to ground plane.

IF2 OUT

IF1 OUT

Rev A7 060203

8-23

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