SAA1575HL

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 SAA1575HL 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 of SAA1575HL 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 of SAA1575HL 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 of SAA1575HL eliminate the need for external glue logic for external memory access.

Each of the 8 GPS channel correlators of SAA1575HL 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.