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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

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

featuremaintainsthephasedetectorwithinitslinearrangeof

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,anddropsto1

µAinshutdown,maximizingoperating

lifeinbattery-poweredsystems.Amplifierbandwidthisuser-

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

1

8

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

FOR INFORMATION PURPOSES ONLY

OBSOLETE:

Contact Linear Technology for Potential Replacement