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AD6411

DECT RF Transceiver

Analog Devices 

AD6411

L2

VCC

BPF1 LNA BPF2

VCC

S1

L1

PA

C1

SAW

C14

C13

LOAD

SYNTH

VCC

L3

C2 R2

R3 L4

TCI

V1

C3

C5

R1

C4

+

REF

+

DC RESTORE

BSW

TXDATA

X2

0...31

32/33

32/34

12/16

PFD

REFERENCE

REGULATOR #1

AD6411

CONTROLLER

INTERFACE

REGULATOR #2

DMOD DATA

C6

SFS

R4 VREF

C7

VBAT

Q1

VBAT

C8

Q2

C9

C10

R6

REF RSSI

C11

R5

VBAT

C12

Figure 1. Functional Block Diagram

PRODUCT OVERVIEW

The AD6411 provides most of the active circuitry required to

realize a complete low power DECT transceiver.

Figure 1 shows the main sections of the AD6411. It consists, in

the receive path, of a UHF mixer and two-stage IF strip with

integrated demodulator and data slicer. The transmit path con-

sists of a VCO, frequency doubler and buffer amplifier.

Channel selection is performed by an on-chip PLL synthesizer.

All AD6411 operating modes can be controlled by parallel con-

trol inputs or the serial interface.

Receive Mixer

The UHF mixer is an improved Gilbert-cell design. The dy-

namic range at the input of the mixer is determined, at the up-

per end, by the maximum input signal level of –16 dBm in 50 Ω

at RFIN up to which the mixer remains linear and a valid RSSI

signal is provided and, at the lower end, by the noise level.

The local oscillator input of the receive mixer is internally pro-

vided by the LO, which is obtained by doubling the on-chip

VCO frequency.

The output of the mixer is single-ended. The nominal conver-

sion gain is specified for operation into a 110.592 MHz or

112.32 MHz SAW IF DECT bandpass filter. The power gain

of 17 dB is measured between the mixer input and the input of

this filter.

IF Circuits and Demodulator

Demodulation is achieved via a PLL. This is shown in detail in

Figure 2. An external manufacturing trim is required to achieve

the required level of frequency accuracy. The approach is to

adjust the capacitor TC1 (with the presence of an unmodulated

carrier) such that the dc level at Pin 3 (DEMOD_DATA) is

equal to the voltage on the external reference pin VREF.

Two demodulation modes are supported. In one mode any

frequency offset due to reference drift or frequency offsets on

the incoming carrier are propagated to the output (referred to as

“Normal” demodulation). The other method is to use a feature

of the DECT system that enables a secondary compensation

circuit to track out frequency offsets (“S-field sampling,” which

is enabled by the pin SFS—active high together with the con-

figuration bit SFM set over the serial interface).

REV. 0

–5–

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