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LTC1340

Low Noise, Voltage-Boosted

Varactor Driver

FREQUENCY (120kHz/DIV)

0dB

1340 TA02

900MHz

Spectral Plot of VCO Output Driven by LTC1340

Resolution Bandwidth = 300Hz

FEATURES

The LTC

5V varactor drive from a single 3V or higher voltage supply.

It includes a low noise amplifier with an internal gain of 2.3

and a self-contained charge pump to generate output volt-

ages above the input supply. The amplifier input stage

includesabuilt-inoffsetvoltagethatallowstheoutputvoltage

to swing to ground without requiring OV on the input. This

feature maintains the phase detector within its linear range of

operation. The LTC1340 requires only three external surface

mount capacitors to implement a complete varactor driver

module.

The LTC1340 features output referred noise of 15

minimizing frequency deviation in PLL frequency synthe-

sizer systems. Supply current is 400

µA typically with a 3V

supply, and drops to 1

µAinshutdown,maximizingoperating

life in battery-powered systems. Amplifier bandwidth is user-

adjustable from 10kHz up to 500kHz and the output typically

sinks or sources 20

µA, allowing fast output signal changes

with a typical varactor load. The amplifier input features rail-

to-rail input common mode range, allowing it

to interface with the output of virtually any phase detector

circuit.

The LTC1340 is available in MS8 and SO-8 packages.

Low Voltage Frequency Synthesizer

LTC1340

PGND

CP

VCO

0V TO 5V

IN

18

7

6

2

3

4

5

3V

1340 TA01

OUT

LOOP

FILTER

SHDN

SHUTDOWN

AGND

270pF

0.1

µF

0.1

µF

PHASE

DETECTOR

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

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Generates 5V Varactor Drive from a 3V Supply

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Wide Supply Voltage Range: 2.7V to 6V

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Requires Only Three External Components

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Micropower Operation: 400

µA at 3V Supply

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Shutdown Mode Drops Supply Current Below 1

µA

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Low Output Noise: 15

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Amplifier Gain: 2.3

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Up to 500kHz Signal Bandwidth

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MS8 and SO-8 Packages

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Very Low Input Bias Current: 10nA Max

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Amplifier Offset Maintains Phase Detector

in Linear Region

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5V Varactor Drive from a Single Li-Ion Cell

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5V Varactor Drive from Three NiCd/NiMH Cells

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Cellular Telephones

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Portable RF Equipment

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Radio Modems

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Wireless Data Transmission