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Does AGC REALLY Necessary in GPS Front-end?

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bobxing

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gps agc

Hi!

In GPS RF Front-end, As the signal is buried in the noise (about 20dB lower), and the noise is rand guass-white thermal noise and unlikely to change, does AGC necessary?

When using 4-bit ADC after the IF AGC, it allows relatively larger input range, then I guess AGC can be omitted, right?

Why commercial chip commonly use 1-2bit ADC, while keep AGC module???


Thanks a lot!
 

gps front-end

Usually, one or two bits GPS RF are used and should be enough. However, if you want to deal with jamming signal, more bits is needed.
 

gps agc

Any idea what is the specs for the jamming signal?
 

agc gps

Yes, I agree with yifen, I think 4-bit A/D also ease the design of AGC. RIGHT?

If the noise power is much higher than the signal , do we still want AGC?
 

how to specify gps frontend

In GPS AGC gain may be used to discriminate between types of interference.
**broken link removed**
 

jamming to noise, agc

Hi,

Higher number of bits for same bandwidth
==> better interference suppression, more gain (for this refer the 1998 IEEE Proceedings)

AGC ==> Is needed so that the reciever does not saturate. It is strictly not needed. but we need more numer of bits. I know at least one rf front end being designed without AGC. I do not know of their performance.
If AGC is not present the signal processing differres a bit an standard algorithms need to be more adaptive. The baseband processing now differs.

Hope this is useful.

B R M
 

    B

    bobxing

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discriminate jamming gps

can you tell me, why set 33% of the logic 1 of the MAG in the ADC side.
 

gps 2 bits adc

1-2 bit ADCs are cheaper (in olden days) when compared to higher bits.
But now ADC are of same price( I suppose) so we can have higher ADC with out external AGC.

Jamming signal can be handled by using SAW filters may not be at the GPS frequency.

Modulation and envelope variation may not be that fast that 1-2 bit ADC is sufficient
 

agc in the front end rf section

AGC may be used to compensate the characteristic variations of the RF stage across a production lot, or compenstate connecting to active/passive antenna with diffent gain.

With just a single fixed design, AGC can be eliminated. But across production lot and any possiblility of usage variations, then AGC is needed.
 

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