LTC1340 Datasheet, PDF (1/8 Pages) Linear Technology – Low Noise, Voltage-Boosted Varactor Driver

FEATURES
s _{Generates 5V Varactor Drive from a 3V Supply}
s _{Wide Supply Voltage Range: 2.7V to 6V}
s _{Requires Only Three External Components}
s _{Micropower Operation: 400µA at 3V Supply}
s _{Shutdown Mode Drops Supply Current Below 1µA}
s _{Low Output Noise: 15µVRMS}
s _{Amplifier Gain: 2.3}
s _{Up to 500kHz Signal Bandwidth}
s _{MS8 and SO-8 Packages}
s _{Very Low Input Bias Current: 10nA Max}
s _{Amplifier Offset Maintains Phase Detector}
in Linear Region
U
APPLICATIONS
s _{5V Varactor Drive from a Single Li-Ion Cell}
s _{5V Varactor Drive from Three NiCd/NiMH Cells}
s _{Cellular Telephones}
s _{Portable RF Equipment}
s _{Radio Modems}
s _{Wireless Data Transmission}
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTC1340
Low Noise, Voltage-Boosted
Varactor Driver
DESCRIPTION
The LTC^®1340 is a varactor diode driver designed to generate
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
includes a built-in offset voltage that allows the output voltage
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 15µV_RMS,
minimizing frequency deviation in PLL frequency synthe-
sizer systems. Supply current is 400µA typically with a 3V
supply, and drops to 1µA in shutdown, maximizing operating
life in battery-powered systems. Amplifier bandwidth is user-
adjustable from 10kHz up to 500kHz and the output typically
sinks or sources 20µA, 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.
TYPICAL APPLICATION
Low Voltage Frequency Synthesizer
3V
PHASE
DETECTOR
0.1µF
2
1
8
V_CC CP AV_CC
0.1µF
LTC1340
5 IN
OUT 7 ^{0V TO 5V}
VCO
LOOP
FILTER
A_V = 2.3
SHDN PGND AGND
3
46
270pF
SHUTDOWN
1340 TA01
Spectral Plot of VCO Output Driven by LTC1340
Resolution Bandwidth = 300Hz
0dB
V_CC = 3V
C_OUT = 270pF
900MHz
FREQUENCY (120kHz/DIV)
1340 TA02
1