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Industry News / Semiconductors / Integrated Circuits / Software & CAD / Subsystems and Systems

A CMOS-based Front-end Downconverter for GPS Applications

Description of a CMOS-based front-end downconverter used to downconvert incoming satellite signals from 1.575 GHz to an intermediate frequency of 1.023 MHz

January 1, 2002
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Product Feature

A CMOS-based Front-end Downconverter for GPS Applications


Valence Semiconductor
Irvine, CA

The industry is striving for single-chip Global Positioning System (GPS) designs given the limited real estate available within cell phones, personal digital assistants (PDA) and other consumer electronic devices. Since GPS designs are typically comprised of a front-end (to receive the satellite signals) and a digital baseband section (to process the signal's information), it is imperative that the baseband and radio utilize the same technological process. The basebands that exist today are typically designed in digital complimentary metal oxide semiconductor (CMOS) technology, while radios have been designed in either bi-polar, bi-CMOS or silicon germanium technologies. If the baseband is fabricated using a process different from the radio portion, then single-chip GPS designs are not possible and the best architecture that can be achieved is a dual-chip system. However, a pure CMOS-based radio has now been developed in deep sub-micron technology that is leading the way to a single-chip system.

The VS7001 device is a CMOS-based front-end downconverter for GPS that downconverts incoming satellite signals (position, location and navigation) from 1.575 GHz to an intermediate frequency (IF) of 1.023 MHz for external GPS basebands to process. The chip provides GPS designers a solution with low power consumption, small die size, low external component count and a high level of integration for implementation in mobile and wireless devices.

Because the VS7001 chip is designed in pure, deep sub-micron CMOS, it provides a number of design advantages that include low cost, robust performance, integration with industry-leading baseband technologies and low power consumption. As a result of the 27 mW total power consumption, the downconverter device can be placed in battery-operated devices that will open many new GPS and mobile connectivity markets. In the future, this new chip will be available in cell phones to enable them to comply with the new FCC Enhanced 911 standard in vehicles to provide navigation capabilities and in PDAs equipped with real-time maps.

Fig. 1 The VS7001 GPS front-end downconverter's block diagram.

VS7001 Architecture

A modified low IF radio architecture was used with an on-chip image-rejection filter for the highest level of integration. Figure 1 shows the VS7001 chip's block diagram. Innovative low power, low noise CMOS circuit design techniques were utilized to obtain the lowest possible power consumption with high performance. In addition to the architecture and circuit-level innovation, this level of integration required careful layout techniques to prevent interference between different blocks.

The new GPS technology has eliminated the need for expensive and bulky surface acoustical wave (SAW) IF filters, or multiple passive components, which other GPS providers use to attenuate image signals and noise. The VS7001 fully integrates all the major components required for the radio, namely the LNA, mixer, IF filter, automatic gain control, quantizer, voltage controlled oscillator and phase-locked loop. The only off-chip components are a crystal, an antenna pre-select filter, and a few resistors and capacitors. Figure 2 shows the IC's pinout diagram. The intended input signal for the VS7001 receiver is the L1 GPS signal at 1.57542 GHz.

Fig. 2 VS7001 pin diagram.

Supporting flexible interfaces, the new VS7001 accommodates several available baseband technologies, including those from industry leading companies such as Sony, Mitsumi and Parthus. Table 1 lists the VS7001 product's performance specifications.

Table 1
Performance Specifications

Input frequency (GHz)

1.57542 GPS L1

IF filters

Internal-no external components required

External LNA gain (dB)

25

Noise figure (dB)

8

Power dissipation at 2.2 V (mW)

27

Clock frequency (MHz)

18.414

Clock input

Crystal or TCXO

Sampled IF output (MHz)

1.023

Output format

Differential or single-ended CMOS

Voltage input (V DC)

2.2 or 3.6

LO phase noise
at 10 kHz
at 1 MHz

-70
-105

Temperature range (°C)

-40 to +85

Package

48-pin TQFP

Applications

The VS7001 downconverter design is ideally suited to penetrate the leading GPS markets worldwide, including in-vehicle navigation, consumer communications and vehicle/freight tracking. Other GPS markets for the VS7001 include surveying and mapping, marine, aviation, agriculture and military. Virtually any GPS application in use today or being planned for the future will benefit from the VS7001 chip's small total footprint and low power consumption. Its ability for total integration with the baseband will enable the GPS function to be implemented in today's ever shrinking mobile equipment to a level not yet seen. The one-chip GPS solution is now entirely achievable.

The VS7001 is offered in a compact 48-pin TQFP package and is available in volume production for $7 to $10 in quantities up to 10,000.

Valence Semiconductor, Irvine, CA (949) 655-4100, www.valencesemi.com.
Circle No. 305

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