LT5502

1

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

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IEEE802.11

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High Speed Wireless LAN

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Wireless Local Loop

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Single 1.8V to 5.25V Supply

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IF Frequency Range: 70MHz to 400MHz

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84dB Limiting IF Gain

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90dB Linear RSSI Range

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7.7MHz Lowpass Output Filter

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Baseband I/Q Amplitude Imbalance: <0.7dB

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4dB Noise Figure

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Low Supply Current: 25mA

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Outputs Biased Up While in Standby

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Shutdown Current: 1

µA

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24-Lead Narrow SSOP Package

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

400MHz Quadrature

IF Demodulator with RSSI

, LTC and LT are registered trademarks of Linear Technology Corporation.

The LT

quadrature IF demodulator. It consists of an IF limiter,

quadrature down mixers, integrated lowpass filters, and

divide-by-two LO buffers. The demodulator provides all

building blocks for demodulation of I and Q baseband

signals with a single supply voltage of 1.8V to 5.25V. The

IF limiter has 84dB small-signal gain, and a built-in receive

signal strength indicator (RSSI) with over 90dB linear

range. The input referred noise-spectral-density is

1.45nV/

√Hz, which is equivalent to a 4dB noise figure

when the input is terminated with a 50

Ω source. The

integrated lowpass output filters act as antialiasing and

pulse-shaping filters for demodulated I/Q-baseband sig-

nals. The 3dB cutoff frequency of the filters is about

7.7MHz. The VCO frequency is required to be twice the

desired operating frequency to provide quadrature local

oscillator (LO) signals to the mixers. The standby mode

provides fast transient response to the receive mode with

reduced supply current when the I/Q outputs are

AC-coupled to a baseband chip.

I/Q Output Swing, RSSI Output vs IF Input Power

IF INPUT POWER (dBm)

–85

1200

1000

800

600

400

200

1.2

1.0

0.8

0.6

0.4

0.2

–70

–55

–40

–25

5502 TA01b

–10

5

EN

+

–

+

–

90

°

0

°

GND

2V

C2

1

µF

C1

1nF

C4

1.8pF

RSSI

ENABLE

2XLO

INPUT

IF

INPUT

R1

240

Ω

C3

22nF

BASEBAND

DIFFERENTIAL

I/Q OUTPUTS

5502 TA01a

÷2

LT5502