The GPS is based on 24 satellites located in six orbital planes at a height of 20 200 km and circle the Earth every 12 h. Each plane is inclined at 55 to the Earth’s equator and contains four satellites. The GPS positioning is based on oneway time-of-arrival ranging. Each satellite sends the universial time (UTC) and navigation data using a spread spectrum code division multiple access (CDMA) technique. A receiver can calculate its own position and speed by correlating the signal delays from any four satellites and combining the result with orbit-correction data sent by the satellites.
Two services are provided by GPS: a precise positioning service (P-code) whose use is restricted to military and a standard positioning service (coarse acquisition, C/A-code), less precise than the P-code but available to everyone. All 24 satellites send on the same two frequencies: L1 is the primary frequency and carries the C/A-code, and L2 is the secondary frequency and carries the P-code. The two frequencies are derived from a 10.23-MHz atomic frequency standard. The frequency of L1 is 1575.42 MHz (154 times the atomic clock) and that of L2 is 1227.6 MHz (120 times the atomic clock). Interference between signals of different satellites is avoided using pseudorandom signals with low cross-correlation for the CDMA modulation. The C/A-code uses 1023 chips Gold codes , . The integrated circuit reported in this work is a low-power RF front-end for a GPS receiver for the 1575.42 MHz civilian L1 band. The immediate application of such an integrated receiver is to provide GPS time reference—GPS positioning will be used to set the correct time zone—for small, portable (wearable) consumer products. Low power consumption is therefore a primary requirement, and the speci?ed power source is a small lithium battery (2.43.5 V). The number and size of external components are also important requirements, not only due to cost, but also the space available. Both requirements must already be addressed during system planning.