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SAA1575HL

Global Positioning System (GPS) baseband processor

Philips Electronics 

Philips Semiconductors

Global Positioning System (GPS)

baseband processor

Product specification

SAA1575HL

1 FEATURES

• Single-chip GPS baseband solution with built-in 16-bit

microcontroller

• All digital, 0.5 micron CMOS technology

• Single power supply with full 3 V operation

• Separate I/O power supply pins for operation with

3 or 5 V external devices

• Up to 30 MHz system clock from on-chip crystal

oscillator or external clock input

• 2 kbytes words internal data memory for fast execution

• External bus for up to 512 kbytes words data memory

and 512 kbytes words program memory

• Programmable external bus timing to match external

memory speed

• Chip selection outputs to reduce glue logic requirements

• Reset controller for power-down detection and servicing

• 8 GPS channel correlators driven by firmware for

flexible GPS correlation algorithms

• 1 second pulse output of GPS time

• 2-bit digital IF GPS signal input synchronized to external

sample clock

• 2 fully duplex UARTs for communication with host

system processor and other devices

• Real-time clock with 32.768 kHz crystal and supply for

low power timekeeping

• Watchdog timer

• Power-down modes under firmware control

• 100-pin LQFP package

• 50 mA supply current (typ.) when 8 GPS channels in

track (approximate).

2 GENERAL DESCRIPTION

The SAA1575HL is an integrated circuit which implements

a complete baseband function for Global Positioning

System (GPS) receivers. It combines a 16-bit Philips

80C51XA microcontroller, 8 GPS channel correlators and

related peripherals in a single IC. Users can implement a

complete GPS receiver using only the SAA1575HL, the

UAA1570HL front-end Philips IC (or similar), external

memory and a few discrete components.

The IC is aimed at low cost applications. A low power

solution was also used where possible, although this was

of secondary importance to cost. The core of the

SAA1575HL operates at 3 V.

However, for compatibility with current automotive

applications, the periphery is supplied from separate pins

and can be operated between 3 and 5 V, as required.

The function of the SAA1575HL is to read the 1 or 2-bit

sampled IF bitstream from a front-end IC and, under

control of firmware on an external ROM, calculate the full

GPS solution. The results are communicated to a host in

National Maritime Electronics Association (NMEA) format

via a standard serial port. A second serial port can be used

to provide differential GPS information to the processor for

more advance applications. In addition, various other

functions are integrated onto the IC such as a real-time

GPS clock, a power-down/reset controller, timer/counters

and a watchdog timer.

To summarise, the SAA1575HL has the following

functional units:

• 16-bit 80C51XA microcontroller core

• 2 kbytes words on-chip SRAM (16-bit words)

• 8 GPS channel correlators

• 2 UARTs

• 8 general purpose I/O lines

• 3 timer/counters

• 1 real-time clock

• 1 watchdog timer

• 1 power-down/reset controller.

The structure is based on a 16-bit microcontroller core

operating on all other units as memory mapped

peripherals and registers. A 16-bit data bus and a 19-bit

address bus are extended to external pins so that external

data and program memory can be accessed. On-chip

decoder circuits eliminate the need for external glue logic

for external memory access.

Each of the 8 GPS channel correlators includes a carrier

Numerically Controlled Oscillator (NCO), PN code

generator, phase rotator and low-pass filter. They

correlate the local PN sequence with the digitized input

GPS signal and generate the filtered correlation result for

the microcontroller. The firmware provided then generates

a navigation solution and provides standard GPS data

outputs to the user.

1999 Jun 04

3

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