Low-Cost, 900MHz, Low-Noise Amplifier

and Downconverter Mixer

6

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Pin Description

NAME

FUNCTION

1, 3, 8,

11, 12, 14

GND

Ground. Connect to ground plane with a low-inductance connection.

2

LNAIN

RF Input to LNA and LNA Bypass Switch. Requires an external matching network and a series

DC-blocking capacitor.

PIN

4

GAIN

Gain Control Logic-Level Input. Drive high to enable the LNA, open the LNA bypass switch, and

increase the receiver’s gain. Drive low to disable the LNA, close the LNA bypass switch, and reduce

the receiver’s gain.

5, 15

6

SHDN

place the device in low-power shutdown mode.

7

LO

Local-Oscillator Input to Downconverter Mixer. Requires a series DC-blocking capacitor and an imped-

ance-setting resistor (typically 75

Ω to ground).

9

IFOUT-

Inverting Side to Downconverter Mixer’s Differential Open-Collector IF Output. Requires a pull-up induc-

10

IFOUT+

Noninverting Side of Downconverter Mixer’s Differential Open-Collector IF Output. Requires a pull-up

13

MIXIN

RF Input to Downconverter Mixer. Requires an external matching network and series DC-blocking

capacitor.

16

LNAOUT

LNA Output. Internally matched to 50

Ω. LNAOUT has an internal blocking capacitor.

LNA

INPUT

880MHz

MAX2685

6pF

6pF

3.3pF

300pF

300pF

LNA

OUTPUT

MIXER

INPUT

880MHz

47pF

12pF

IF

OUTPUT

80MHz

1

2

3

4

5

0.1

µF

12nH

6

7

330pF

75

Ω

8

12

13

14

15

16

11

10

9

GND

LNAOUT

MIXIN

GND

*OPTIONAL FOR BROADBAND MATCH.

R*

IFOUT-

IFOUT+

680nH

820nH

LO

LNAIN

47pF

GAIN

SHDN

GND

GND

GND

GND

GAIN-

CONTROL

INPUT

SHUTDOWN

INPUT

1000pF

LO

INPUT

960MHz

Figure 1. Typical Operating Circuit