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 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.