A review of current state-of-the-art GNSS radio frequency (RF) front-end receivers is required to establish the starting point in the creation of any electronic device. Not only have scientific papers been published on GNSS front-end receivers but a number of these devices are also on the market. Thus, both scientific papers and commercial receivers will be analysed.
Scientific Papers
An integrated GPS front-end was first mentioned in scientific literature in 1992[Benton92]. It was designed with gallium arsenide (GaAs) technology and was capable of a 54dB gain at 1600mW, with a low noise amplifier (LNA) of 2.7dB, as shown in Table 1-4.
As usual, GaAs technology played an important role in the early stages of these devices. As soon as bipolar and complementary metal-oxide semiconductor (CMOS) performance improved, designs adapted these technologies. Thus, from 1997 on, all published designs have been either bipolar, CMOS, or silicon germanium (SiGe). Although CMOS makes up the majority of designs, two bipolar references, [Kucera98] and [Cloutier99], have been found and only one of the designs uses SiGe technology[Sivonen02]. There is still a debate about which technology, CMOS or SiGe, is the most suitable for RF applications. Although SiGe performs better than CMOS when it comes to RF, the latter is the more affordable of the two. Furthermore, the lowest noise figure (NF) for the LNA is achieved with SiGe technology[Sivonen02].
A brief analysis of the front-ends can be found in Table 1-4. As reflected in the table, some of the front-ends make use of an external LNA as in [Murphy97] and [Piazza98]. Although the LNA has a high gain, it also presents high NF throughout the entire system. Other designs such as [Shahani97], [Svelto00], and [Sivonen02] do not integrate a phased-lock loop (PLL), voltage-controlled oscillator (VCO), or analogue to digital converter (ADC) and consequently consume less power. Due to integration complexity, most of them have both external intermediate frequency (IF) filters and RF filters[Sainz05]. Finally, the digitalization for most of the designs is carried out by a 1bit ADC.
[Chen05] and [Sahu05], which employed CMOS 0.18um and CMOS 90nm respectively, do not match the gain and NF performance found in [Shaeffer98] and [Kadoyama04], both of which also made use of CMOS technology and are highly integrated. The second one exhibits lower power consumption and includes the correlator and processor in the same chip, making it suitable for mobile applications. The main characteristics of the GPS front-ends collected here are summarized in Table 1-4.
TABLE 1-4 State-of-the-art GPS front-ends
|
LNA |
chip |
|
|
|
Power |
|
|
|
|
|
|
|
NF |
NF |
Gain |
P1dB |
IIP3 |
consumption |
|
|
External |
|
|
Reference |
[dB] |
[dB] |
[dB] |
[dBm] |
[dBm] |
[mW] |
Technology |
Architecture |
components |
ADC |
|
[Benton92] |
2.7 |
— |
54 |
— |
— |
1600@8V |
GaAs |
Digit. IF |
— |
— |
|
[Murphy97] |
2 |
6.1 |
107 |
-29 |
— |
81@3V |
Bipolar |
Hetero |
Filters, LNA, |
1bit |
|
PLL |
||||||||||
|
[Shahani97] |
3.8 |
— |
13 |
— |
— |
12@1.5V |
CMOS 0.5|m |
Digit. IF |
Filters, VCO, PLL, ADC |
— |
|
[Kucera98] |
2.3 |
3.5 |
20 |
— |
— |
16.5@3V |
Bipolar |
— |
— |
— |
|
[Piazza98] |
1.5 |
8.1 |
94.5 |
-28 |
— |
32@3V |
BiCMOS 1|m |
Hetero |
2 filters, LNA |
1bit |
|
[Shaeffer98] |
2.4 |
4.1 |
98 |
-58 |
— |
112@3V |
CMOS 0.5|m |
Digit IF |
Filters |
1bit |
|
[Cloutier99] |
3 |
4 |
120 |
— |
-26 |
49@3V |
Bipolar |
Filters |
2bit |
|
|
[Meng98] |
2.4 |
5.4 |
82 |
— |
— |
79 |
CMOS 0.5| m |
Digit. IF |
VCO, PLL |
1bit |
|
[SveltoOO] |
— |
3.8 |
40 |
— |
-25.5 |
8@2.8V |
CMOS 0.35| m |
— |
Filters, VCO, PLL, ADC |
— |
|
[Sivonen02] |
1.38 |
2.7 |
25.8 |
-27.6 |
-14.5 |
15.3@2.7V |
SiGe |
— |
Filters, PLL, ADC |
— |
|
[Steyaert02] |
1.5 |
— |
15.5 |
— |
-6 |
— |
CMOS 0.25| m |
— |
— |
— |
|
[Kadoyama04] |
— |
4 |
110 |
— |
— |
27@1.8V |
CMOS 0.18|m |
— |
Filters |
1bit |
|
[Chen05] |
— |
4.13 |
27.7 |
-29.9 |
-19 |
22.2@1.8V |
CMOS 0.18|m |
— |
— |
— |
|
[Sahu05] |
1.8 |
2 |
38 |
— |
— |
60@1.4V |
CMOS 90nm |
— |
— |
— |
|
[Berenguer06]* |
3.2 |
3.7 |
103 |
— |
— |
62@3V |
SiGe 0.35| m |
Low IF |
Filters |
1bit |
The latest reported GPS front-end is the only device that could currently be applied to GPS and Galileo. It encompasses 0.35um SiGe technology, exhibits a high voltage gain of 103dB, a single-sideband modulation (SSB) noise level of 3.7dB (which makes it suitable for high-sensitivity applications), a power consumption of only 62mW from a 3V supply, and a minimal amount of external components (which makes it suitable for mobile applications).
Commercial Receivers
Many semiconductor companies offer a GPS receiver chipset. Out of all the reviewed commercial receivers, only [ublox ATR0630_35] includes the baseband processor together with the RF front-end; the rest are mostly composed of two integrated circuits (ICs): the front-end and the processor. A comparison of characteristics of front-ends from different manufacturers is summarised in Table 1-5.
Although most devices described in scientific papers are designed with CMOS, most commercial front-ends use bipolar technology. Not all systems are fully integrated, since the LNA is external in some cases. Moreover, mainly 1bit and 2bit ADCs are used for digitalisation.
TABLE 1-5 State-of-the-art GPS commercial IC front-ends
|
Reference |
VCC [V] |
Power [mW] |
Gain [dB] |
NF [dB] |
Bit nr. |
Comments |
|
[Atmel ATR0603] |
3 |
38 |
76 |
8 |
1 |
External LNA, single conversion, AGC |
|
[Freescale MRFIC1505] |
3 |
84 |
105 |
2 |
Internal LNA, double conversion, AGC, no ADC |
|
|
[MAXIM MAX2741] |
3 |
90 |
80 |
4.7 |
2/3 |
Internal LNA, double conversion, AGC |
|
[MAXIM MAX2769] |
3 |
54 |
96 |
1.4 |
2/3 |
Two internal LNA, single conversion, ready for Galileo |
|
[PHILIPS UAA1570HL] |
3 |
165 |
148 |
4.5 |
1 |
Two internal LNA, double conversion, AGC |
|
[SiGe SE4120L] |
3 |
30 |
18 |
>1.6 |
Internal LNA, ready for Galileo, multibit serialized digital I/Q output |
|
|
[SONY CXA1951AQ] |
3 |
90 |
100 |
7 |
— |
Internal LNA, double conversion, no ADC |
|
[ST STB5610] |
3.3 |
122 |
139 |
3 |
1 |
Internal and external LNA, single conversion |
|
[ublox ATR0630_35] |
3 |
87 |
90 |
6.8 |
1.5 |
Integrated solution including RF, IF filter, and baseband |
|
[uNAV un8021C] |
3 |
62 |
~106 |
20 |
2 |
Internal LNA, single conversion |
|
[zarlink GP2015] |
3 |
173 |
120 |
9 |
2 |
External LNA, triple conversion, AGC |
The [ST STB5610] front-end presents the best gain-to-noise figure ratio with a gain of 139dB and an NF of 3dB, achieved at a rate of consumption as high as 122mW. [Freescale MRFIC1505] also has a high gain of 105dB with a low NF of 2dB. On the other hand, [uNAV un8021C] achieves a gain of 106dB while consuming 62mW. However, it presents a high NF of 20dB. [SiGe SE4120L] and [MAXIM MAX2769] are dual front-ends currently ready for GPS and Galileo applications.
Components
A thorough analysis of available key components of a front-end such as the LNA, mixer, and PLL is required prior to the definition of the front-end blocks to be designed. The reviewed scientific papers and datasheets failed to provide all required information.
First, characteristics of some LNAs of the previously mentioned front-ends are shown in Table 1-6. Most of the designs are single-ended designs and work with a power supply between 1.5V and 3.3V. The most important characteristics to consider are noise, gain, and power consumption. The highest gain is achieved by [Shaeffer97], which exhibits 20dB with a 3.5dB noise level. On the other hand, the lowest noise level is achieved in the first LNA of the two included in [MAXIM MAX2769], which exhibits 0.83dB for a 19dB gain.
Table 1-7 shows the characteristics of the mixers of some of the previously mentioned GPS front-ends. Conversion gain, noise, and power consumption are the key parameters for this component. The highest gain of 30dB and the lowest noise level of 5.5dB are obtained by [ST STB5610], made possible by a preamplifying stage prior to the mixer itself.
TABLE 1-6 State-of-the-art LNAs for GPS
|
Reference |
Vdd [V] |
Current [mA] |
Gain [dB] |
NF [dB] |
P-1dB [dBm] |
IIP3 [dBm] |
|
[Shaeffer97] |
1.5 |
20 |
22 |
3.5 |
-24.5 |
-9.3 |
|
[Shahani97] |
1.5 |
8 |
17 |
3.8 |
-21 |
-6 |
|
[Shaeffer98] |
2.5 |
5 |
16 |
2.4 |
-23 |
-8 |
|
[Piazza-Orsati98] |
2.5 |
18 |
14 |
2 |
-16.8 |
-1.5 |
|
[Sanav02] |
2.5 |
4.5 |
19.5 |
1.3 |
— |
— |
|
[MaximOl] |
3 |
5.8 |
15 |
1.5 |
-18 |
-3 |
|
[Alvarado07] |
3 |
8 |
18 |
3.3 |
-24 |
— |
|
[MAXIM MAX2769] |
3 |
— |
19 |
0.83 |
— |
-1.1 |
|
[MAXIM MAX2769] |
3 |
— |
13 |
1.14 |
— |
1 |
|
[PHILIPS UAA1570HL] |
3 |
— |
15.5 |
3.7 |
-22 |
-13 |
|
[ST STB5610] |
3.3 |
— |
19 |
3 |
— |
-20 |
|
[Freescale MRFIC1505] |
3 |
— |
15 |
2 |
-14 |
— |
|
[ublox ATR0610] |
3 |
3.3 |
16 |
1.6 |
-9 |
-1 |
TABLE 1-7 State-of-the-art GPS mixers
|
Reference |
Vdd [V] |
Current [mA] |
Gain [dB] |
NF [dB] |
P-1dB [dBm] |
IIP3 [dBm] |
|
[Kilicaslan97] |
— |
— |
3.35 |
9 |
-12 |
2.17 |
|
[Sullivan97] |
3 |
13 |
6.5 |
8.5 |
-12 |
-3 |
|
[Wang88] |
1 |
— |
6 |
9.6 |
-5 |
10 |
|
[PHILIPS UAA1570HL] |
3 |
— |
17.7 |
12 |
-25.4 |
-16.3 |
|
[zarlink GP2015] |
3 |
— |
18 |
9 |
-16 |
— |
|
[Atmel ATR0603] |
3 |
— |
~20 |
6.9 |
— |
— |
|
[ST STB5610] |
3 |
— |
30 |
5.5 |
— |
-19 |
|
[SONY CXA1951AQ] |
3 |
— |
16 |
7 |
— |
— |
|
[Freescale MRFIC1505] |
3 |
— |
14 |
13 |
-27 |
— |
Finally, Table 1-8 includes not only PLLs of GPS front-ends, but also PLLs of other applications working at similar frequencies. The main parameters to take into account are the phase noise and the power consumption of the device.
Summary
Key parameters useful in comparing the quality of front-ends are gain, noise level, power consumption, integration ratio, and size. Thus, sensitivity, required space, and battery life can be determined. A comparison of available front-ends is worthwhile to set realistic competitive requirements for the desired front-end.
Most commercial front-ends have a high gain exceeding 100dB. The high gain is achieved at a cost of either a high noise level or high power consumption. The same can be seen with designs published in scientific papers; high gain is obtained at a cost of power or noise. However, the gain is lower than that found in commercial receivers.
TABLE 1-8 State-of-the-art PLLs for GPS
|
Reference |
Vdd [V] |
PN [dBc/Hz] |
Current [mA] |
|
[Nhat92] |
5 |
-88 @ 100kHz |
14 |
|
[Craninckx95] |
3 |
-115 @ 200kHz |
8 |
|
[Craninckx98] |
3 |
-123 @ 600kHz |
3.7 |
|
[Hajimiri99] |
3 |
-125 @ 600kHz |
16 |
|
[RogersOO] |
3.3 |
-96 @ 100kHz |
6 |
|
[PHILIPS UAA1570HL] |
3 |
-72 @ 10kHz |
— |
|
[ST STB5610] |
3 |
-60 @ 10kHz |
— |
|
[Atmel ATR0603] |
3 |
-100 @ 1kHz |
— |
|
[zarlink GP2015] |
3 |
-88 @ 100kHz |
— |
High power consumption means shorter battery life and therefore less mobility. However, many applications are not power critical, as in the automotive industry, where the battery of the car could be used. A high noise level could mean lower receiver sensitivity, which is not a drawback in open spaces such as hiking paths free of trees or on the sea, where the battery of a mobile device plays a more important role. However, many applications require long battery life and high sensitivity, which essentially calls for a front-end with a high gain, low noise, and low power consumption.
