GPS and Galileo by Jaizki Mendizabal Samper & Roc Berenguer Pérez & Juan Meléndez Lagunilla

Author:Jaizki Mendizabal Samper & Roc Berenguer Pérez & Juan Meléndez Lagunilla
Language: eng
Format: epub
Publisher: McGraw-Hill Education
Published: 2009-03-14T16:00:00+00:00

S11

< –10

–20.2

dB

OIP3

1.5

0.5

dBm

Gain

23

18.1

dB

NF

6.2

5.6

dB

Current

<13

5.9

mA

3.4 IF Limiting Amplifiers and Filters

The design of two IF LC filters is covered in the IF stage. The first one is located next to the RF down-conversion mixer. The second one is located between the first and second IF limiting amplifiers (see Figure 3-1). The IF filters provide the following functions:

They define and shape the noise bandwidth to be amplitude-quantized by the 1bit ADC.

They provide the required selectivity to protect the IF limiting input from spurious signals that pass through the RF SAW filters, typically 20MHz wide.

They attenuate undesired second mixer output products, such as the LO leakage or mixer second harmonics, to levels that will not block the IF limiter amplifier.

They can reject spurious common mode and/or differential signals generated by high-level on-chip sources, such as reference clock harmonics.

Two IF limiting amplifiers have been considered in the system analysis. Both are preceded by an LC filter, which is located next to the mixer and the first amplifier respectively. They provide the gain required to digitalise the incoming GPS signal. The noise figure is not a key parameter because of its low contribution to the total noise, as stated by the Friis equation [Razavi97], since it is not included in the early stages of the front-end, but after the LNA, the RF amplifier, and the down-conversion mixer.

Figure 3-17 shows the basic cell of the IF amplifier. It is a differential common source architecture due to its high voltage gain as well as its

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