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PDF DCS1800 Data sheet ( Hoja de datos )
| Número de pieza | DCS1800 | |
| Descripción | Triple-band VCO for GSM900/DCS1800/PCS1900 | |
| Fabricantes | NSC | |
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January 2004
LMX2604
Triple-band VCO for GSM900/DCS1800/PCS1900
General Description
The LMX2604 is a fully integrated VCO (Voltage-Controlled
Oscillator) IC designed for GSM900/DCS1800/PCS1900
triple-band application. The IC is ideal for use in the trans-
mitter modulation loop by providing extremely small form
factor and low phase noise. The IC has two VCOs, one for
GSM and a second for DCS/PCS. The IC has two separate
buffer amplifiers to drive an external high power amplifier,
one for GSM900 band and the other one for DCS1800/
PCS1900 bands. The IC also has a differential buffer ampli-
fier to drive a mixer for the offset PLL.
The resonant circuits of the VCOs are fully integrated in the
chip to ease the application of the IC. The high quality factor
of the embedded tank circuit achieves very low phase noise
characteristics at the VCO output. The only required external
components are a couple of supply bypass capacitors and
matching components.
A control pin for controlling the oscillation frequency is
shared by the two VCOs.
The LMX2604 IC is provided in a 20-pin 4x4 LLP (Leadless
Leadframe package).
Features
n On-chip Triple-band RF VCOs
GSM: 880 MHz to 915 MHz
DCS: 1710 MHz to 1785 MHz
PCS: 1850 MHz to 1910 MHz
n On-chip tank circuit
n Low phase noise
— -167 dBc/Hz @ 20 MHz offset in GSM band
— -163 dBc/Hz @ 20 MHz offset in DCS band
— -162 dBc/Hz @ 20 MHz offset in PCS band
n High output power
— +6 dBm in GSM mode
— +6 dBm in DCS and PCS mode
n Low current consumption
— 18 mA in GSM mode
— 15 mA in DCS and PCS mode
n +2.6 V to +3.0 V supply voltage
n 0.25 µm RF CMOS process
n Small 20-pin 4x4 LLP package
Applications
n Transmit VCO for GSM, DCS, and PCS
n Closed loop modulation systems
Functional Block Diagram
FastLock™ is a trademark of National Semiconductor Corporation.
TRI-STATE® is a registered trademark of National Semiconductor Corporation.
© 2004 National Semiconductor Corporation DS200661
20066101
www.national.com
1 page  
Typical Performance Characteristics : Phase Noise
Typical phase noise characteristics in GSM band
Typical phase noise characteristics in DCS band
20066161
20066162
5 www.national.com
5 Page 
Functional Description
PRODUCT DESCRIPTION
The LMX2604 IC has two VCOs, which are configured as an
LC resonant oscillator. The active components and tank
elements are all integrated on the IC. The oscillator core and
the tank circuit are designed to be immune to external noise
such as supply and load variation. The IC is easy-to-use and
occupies extremely small area in the board.
Two output amplifiers are also integrated to deliver high
output power of +6 dBm in GSM/DCS/PCS applications. The
amplifiers isolate the oscillator cores from the external load,
and drive the external 50 ohm load. The output driver is
designed to have low noise floor and to reduce pulling by
load variation. An additional amplifier to drive the mixer in the
transmit PLL is also provided. Only an attenuator composed
of a few passive elements is necessary to meet the power
level of the mixer input of the transmit PLL.
The frequency of the oscillator is controlled by the CPin pin,
which is internally connected to the varactor. This control pin
is connected to the loop filter of the modulation loop in the
transmit path. Any additional noise on this tuning input is
directly translated into FM noise, which can degrade the
phase noise characteristics of the oscillator. Typically, the
loop filter of the PLL provides an appropriately low imped-
ance source at its output and thus proper additional filtering
stage is often required to reduce the high frequency noise
and spurious signals.
FREQUENCY SELECTION AND POWER DOWN
CONTROL
The BSW pin selects the operating frequency band. The
table below shows the appropriate settings with the CE pin.
CE
Low
Low
High
High
BSW
Low
High
Low
High
Output
X
X
Low Band (GSM)
High Band (DCS/PCS)
In real implementation, the component values of the tank
circuit vary from the nominal value. The IC has built-in circuit
to track the variation and compensate that kind of the varia-
tion during normal operation. This self-correction algorithm
does not require any external control signal and elements.
The figure below shows an application circuit of the
LMX2604. The LMX2604 is developed for the use in a GSM
handset as part of the transmitter PLL. To complete the
offset PLL in the transmit path, several passive elements for
the external loop filter should be also provided. The charge
pump output port of the external transceiver IC is fed to the
CPin pin.
The locking process of the LMX2604 is composed of two
stages. First, the internal control circuitry of the LMX2604
controls the fast frequency acquisition behavior of the
LMX2604. After the frequency acquisition, the whole loop
enters in its normal operating mode.
Application Circuit of LMX2604
20066172
11 www.national.com
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| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet DCS1800.PDF ] | |
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