ad6402 Analog Devices, Inc., ad6402 Datasheet - Page 7

• Manufacturer Part Number: ad6402
• Description: Transceiver Subsystem
• Manufacturer: Analog Devices, Inc.

supply current levels when not allocated to an active transmit or
receive timeslot in a TDMA system.. The respective transmit
and receive blocks can be turned on only as needed thereby
reducing power consumption and extending battery life of
handheld terminals.
The component selection in Figure 5 is explained as follows:
The IF input is driven from the output of a SAW filter via an
impedance matching circuit as shown. This matching minimizes
the insertion loss of the filter and follows the filter manufactur-
ers recommendations. The tank circuit shown uses two varactor
diodes. One diode (D3) is biased by the output of the IF PLL
loop filter and ensures that the IF VCO frequency is correctly
centered. The second diode is provided to enable a modulation
signal, which is generated at the output of the on-chip op amp
(MODOUT), to be coupled into the VCO tank and thereby
implement a modulation of the VCO frequency. In the case of
DECT, the IF VCO control loop is opened while the VCO is
being modulated by the transmit bit stream. The loop is opened
by tri-stating the output of the IF VCO PLL charge pump.
The exact component values used around the modulation am-
plifier will be determined by the amount of attenuation required
for suppression of baseband transmit spurii and images. These
artifacts are usually present if the baseband FSK signal is gener-
ated by a ROMDAC. In most instances a second or third order
Bessel or Butterworth filter will be required.
A capacitor to ground is required to be connected to COFF.
This capacitor stores the demodulator charge-pump voltage
required to lock the demodulator VCO to the reference fre-
quency. The dynamic response of the demodulator loop is con-
trolled by selection of the values for C45 and R22 which are
connected in series to CFILT. These components determine the
REV. 0
V
IFIN
TUNE
150nH
C69
1nF
C25
1nF
L5
1.2k
C50
4.7nF
R26
1
2
3
4
5
B4535
47pF
C42
D3
SMV
1204-37
10
9
8
7
6
C41
8pF
D2
240
R21
L6
150nH
100nH
V
CC
L7
SMV
1204-36
Figure 5. Application Circuit for DECT GFSK Transceiver
C44
1nF
L11
39nH
VRF
12pF
VREF
VIF
IFC2
IFC1
IFC0
TXIF+
TXIF–
C30
150pF
100nF
C10
1nF
C43
C44
100nF
C28
C29
1nF
1nF
IFGND
VCOGND
CTL3
CTL2
CTL1
TXOUT
TXOUTB
IFIN
VBAT
VREG
SLREF
VCO
AD6402
330
R16
IFVCC1
REF
–7–
REG
transfer characteristic of the loop filter and hence the lock time,
settling time and bandwidth of the loop. REXT should use the
recommended value as shown.
Finally, the demodulator is followed by a voltage follower,
which is configured as a data filter. This data filter is used to
bandlimit the FM noise generated in the demodulator. It also
attenuates undesired adjacent channel interferers. The compo-
nent values chosen will be a trade-off between the amount of
band limiting required and attenuation of the in-band desired
signal.
DECT Application Circuit Notes (Figure 5)
1. Signal Description
2. Typical IF input sensitivity referred to the input of SAW
3. TxBB filter is user configurable. In the above application, the
VRF: Regulated Supply Voltage; Nominal Value 2.85 V.
V
VTUNE: Synthesizer Control Voltage; Range dependent on
loop filter and synth charge pump compliance.
TXBB: Baseband transmit modulation voltage; typically
SLREF 0.7 V
RCLK: Reference clock for PLL demodulator; 13.824 MHz
(2nd IF frequency = (N/M)
M = 2. Maximum 2nd IF = c.26 MHz)
filter for the above application will be –72 dBm.
filter is implemented to remove images generated by ROM
DAC baseband signal generators. Other implementations are
possible including passive pulse shaping circuits which elimi-
nate the need for such filtering.
/3,/5
CC
: Unregulated battery voltage; 3.1 V–4.5 V
IFVCC2
MODOUT
CP
C71
1nF
CP
PD
CP
FMMOD1
FMMOD2
PLLGND
PLLOUT
PLLVCC
REFSEL
REFIN
DFILP
DOUT
REXT
CFILT
COFF
RSSI
100nF
C32
33pF
R10
2k
4.7k
C12
100pF
Frclk where N = 3 or 5, and
R8
C11
100pF
C52
131nF
C45
C13
1nF
R30
2k
VRF
3.3nF
330
R28
C4
330
R22
1k
R9
10k
C58
47pF
R17
AD6402
C51
180pF
330
R32
C31
4.7k
R70
R35
C14
68pF
RXBB
RSSI
RCLK
TXBB