EVAL-ADF7021-VDB2Z Analog Devices Inc, EVAL-ADF7021-VDB2Z Datasheet - Page 26

• Manufacturer Part Number: EVAL-ADF7021-VDB2Z
• Description: 868 - 870MHz - EVALUATION BOARD
• Manufacturer: Analog Devices Inc
• Type: Transceiverr

Specifications of EVAL-ADF7021-VDB2Z

• Frequency: 868MHz ~ 870MHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: ADF7021
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADF7021-V
The signal mapping of the input binary transmit data to the
three-level convolutional output is shown in Table 9. The
convolutional encoder restricts the maximum number of
sequential +1s or −1s to two and delivers an equal number of
+1s and −1s to the FSK modulator, thus ensuring equal spectral
energy in both RF sidebands.
Table 9. Three-Level Signal Mapping of the Convolutional
Encoder
TxDATA
Precoder
Output
Encoder
Output
Another property of this encoding scheme is that the trans-
mitted symbol sequence is dc-free, which facilitates symbol
detection and frequency measurement in the receiver. In
addition, no code rate loss is associated with this three-level
convolutional encoder; that is, the transmitted symbol rate is
equal to the data rate presented at the transmit data input.
3FSK is selected by setting the MODULATION_SCHEME bits
(Register 2, Bits[DB6:DB4]) to 010. It can also be used with
raised cosine filtering to further increase the spectral efficiency
of the transmit signal.
Four-Level Frequency Shift Keying (4FSK)
In 4FSK modulation, two bits per symbol spectral efficiency is
realized by mapping consecutive input bit-pairs in the Tx data
bit stream to one of four possible symbols (−3, −1, +1, +3). Thus,
the transmitted symbol rate is half the input bit rate. These
symbols are mapped to equally spaced discrete frequencies
centered on the RF carrier at
where f
DEVIATION bits (Bits[DB27:DB19] in Register 2) and is also
equal to half the frequency spacing between adjacent symbols.
By minimizing the separation between symbol frequencies,
4FSK can have high spectral efficiency. The bit-to-symbol
mapping for 4FSK is gray coded and is shown in Figure 43.
FREQUENCIES
−3f
SYMBOL
DEV
DEV
is programmed using the Tx_FREQUENCY_
, −1f
1
1
+1
Tx DATA
DEV
Figure 43. 4FSK Bit-to-Symbol Mapping
+3
–3
+
–
0
0
0
f
f
f
f
, +1f
DEV
DEV
DEV
DEV
f
DEV
1
0
−1
0
, and +3f
1
1
+1
0
0
0
0
DEV
0
1
0
1
0
1
1
1
+1
0
0
1
0
1
0
1
0
1
Rev. 0 | Page 26 of 60
t
1
0
−1
The inner deviation frequencies (+f
the Tx_FREQUENCY_DEVIATION bits (Bits[DB27:DB19] in
Register 2). The outer deviation frequencies are automatically
set to three times the inner deviation frequency.
The transmit clock from Pin TxRxCLK is available after writing
to Register 3 in the power-up sequence for receive mode. The
MSB of the first symbol should be clocked into the ADF7021-V
on the first transmit clock pulse from the ADF7021-V after
writing to Register 3. See Figure 6 and Figure 7 for more timing
information; see Figure 54 and Figure 55 for the power-up
sequences.
Oversampled 2FSK
In oversampled 2FSK, there is no data clock from the TxRxCLK
pin. Instead, the transmit data at the TxRxDATA pin is sampled
at 32 times the programmed rate.
Oversampled 2FSK is the only modulation mode that can be
used with the UART mode interface for data transmission (see
the Interfacing to a Microcontroller/DSP section for more
information).
SPECTRAL SHAPING
Gaussian or raised cosine filtering can be used to improve
transmit spectral efficiency. The ADF7021-V supports Gaussian
filtering (bandwidth time [BT] = 0.5) on 2FSK modulation.
Raised cosine filtering can be used with 2FSK, 3FSK, or 4FSK
modulation. The roll-off factor (alpha) of the raised cosine filter
has programmable options of 0.5 and 0.7. Both the Gaussian
and raised cosine filters are implemented using linear phase
digital filter architectures that deliver precise control over the
BT and alpha filter parameters, and guarantee a transmit spectrum
that is very stable over temperature and supply variation.
Gaussian Frequency Shift Keying (GFSK)
Gaussian frequency shift keying reduces the bandwidth occupied
by the transmitted spectrum by digitally prefiltering the transmit
data. The BT product of the Gaussian filter used is 0.5.
Gaussian filtering can be used only with 2FSK modulation. GFSK
is selected by setting Register 2, Bits[DB6:DB4] to 001.
Raised Cosine Filtering
Raised cosine filtering provides digital prefiltering of the transmit
data by using a raised cosine filter with a roll-off factor (alpha)
of either 0.5 or 0.7. The alpha is set to 0.5 by default, but the
raised cosine filter bandwidth can be increased to provide less
aggressive data filtering by using an alpha of 0.7 (set Register 2,
Bit DB30 to Logic 1). Raised cosine filtering can be used with
2FSK, 3FSK, and 4FSK modulation.
Raised cosine filtering is enabled by setting Register 2,
Bits[DB6:DB4] as shown in Table 10.
DEV
and −f
DEV
) are set using