ata5724p3c-tkqy ATMEL Corporation, ata5724p3c-tkqy Datasheet - Page 8

• Manufacturer Part Number: ata5724p3c-tkqy
• Description: Uhf Ask/fsk Receiver
• Manufacturer: ATMEL Corporation

4.3
8
FSK/ASK Demodulator and Data Filter
Atmel ATA5723C/ATA5724C/ATA5728C
The signal coming from the RSSI amplifier is converted into the raw data signal by the
ASK/FSK demodulator. The operating mode of the demodulator is set using the bit ASK/_FSK
in the OPMODE register. Logic L sets the demodulator to FSK, applying H to ASK mode.
In ASK mode an automatic threshold control circuit (ATC) is employed to set the detection ref-
erence voltage to a value where a good signal to noise ratio is achieved. This circuit also
implements the effective suppression of any kind of in-band noise signals or competing trans-
mitters. If the S/N (ratio to suppress in-band noise signals) exceeds about 10dB the data
signal can be detected properly. However, better values are found for many modulation
schemes of the competing transmitter.
The FSK demodulator is intended to be used for an FSK deviation of 10kHz
The data signal in FSK mode can be detected if the S/N (ratio to suppress in-band noise sig-
nals) exceeds about 2 dB. This value is valid for all modulation schemes of a disturber signal.
The output signal of the demodulator is filtered by the data filter before it is fed into the digital
signal processing circuit. The data filter improves the S/N ratio as its pass-band can be
adopted to the characteristics of the data signal. The data filter consists of a 1
high-pass and a 2
The high-pass filter cut-off frequency is defined by an external capacitor connected to pin
CDEM. The cut-off frequency of the high-pass filter is defined by the following formula:
In self-polling mode the data filter must settle very rapidly to achieve a low current consump-
tion. Therefore, CDEM cannot be increased to very high values if self-polling is used. On the
other hand, CDEM must be large enough to meet the data filter requirements according to the
data signal. Recommended values for CDEM are given in the electrical characteristics.
The cut-off frequency of the low-pass filter is defined by the selected baud-rate range
(BR_Range). The BR_Range is defined in the OPMODE register (refer to
uring the Receiver” on page
used.
The Atmel
the DC level of the data signal is 50%. This is valid for Manchester and Bi-phase coding. If
other modulation schemes are used, the DC level should always remain within the range of
V
condition.
Each BR_Range is also defined by a minimum and a maximum edge-to-edge time (t
These limits are defined in the electrical characteristics. They should not be exceeded to main-
tain full sensitivity of the receiver.
fcu_DF
DC_min
= 33% and V
=
®
------------------------------------------------------------ -
2
ATA5723C/ATA5724C/ATA5728C is designed to operate with data coding where
nd
30 k
order low-pass filter.
1
DC_max
CDEM
25). The BR_Range must be set in accordance to the baud-rate
= 66%. The sensitivity may be reduced by up to 2dB in that
Section 11. “Config-
9248A–RKE–09/11
f 100kHz.
st
ee_sig
order
).