ATA5724 ATMEL [ATMEL Corporation], ATA5724 Datasheet - Page 9

• Manufacturer Part Number: ATA5724
• Description: UHF ASK/FSK Receiver
• Manufacturer: ATMEL [ATMEL Corporation]

5. Receiving Characteristics
9106E–RKE–07/08
The RF receiver ATA5723/ATA5724/ATA5728 can be operated with and without a SAW
front-end filter. In a typical automotive application, a SAW filter is used to achieve better selectiv-
ity and large signal capability. The receiving frequency response without a SAW front-end filter is
illustrated in
relates to ASK mode. FSK mode exhibits a similar behavior. The plots are printed relatively to
the maximum sensitivity. If a SAW filter is used, an insertion loss of about 3 dB must be consid-
ered, but the overall selectivity is much better.
When designing the system in terms of receiving bandwidth, the LO deviation must be consid-
ered as it also determines the IF center frequency. The total LO deviation is calculated, to be the
sum of the deviation of the crystal and the XTO deviation of the ATA5723/ATA5724/ATA5728.
Low-cost crystals are specified to be within ±90 ppm over tolerance, temperature, and aging.
The XTO deviation of the ATA5723/ATA5724/ATA5728 is an additional deviation due to the
XTO circuit. This deviation is specified to be ±10 ppm worst case for a crystal with CM = 7 fF. If
a crystal of ±90 ppm is used, the total deviation is ±100 ppm in that case. Note that the receiving
bandwidth and the IF-filter bandwidth are equivalent in ASK mode but not in FSK mode.
Figure 5-1.
Figure 5-1
-10
-20
-30
-40
-50
-60
-70
10
0
Narrow Band Receiving Frequency Response ATA5724
430
431
“Narrow Band Receiving Frequency Response ATA5724”. This example
Image Rejection versus RF Frequency
432
433
(MHz)
ATA5723/ATA5724/ATA5728
434
435
436
437
438
4.5V -40
5V -40
5.5V -40
4.5V 25
5V 25
5.5V 25
4.5V 105
5V 105
5.5V 105
˚
˚
C
C
˚
˚
˚
˚
˚
C
C
C
C
C
˚
˚
C
C
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