AD7011

REV. B

–9–

I

Q

Figure 10.

π/4 DQPSK Constellation Diagram

Figure 10 illustrates the

π/4 DQPSK constellation diagram as

cosine filters (

α = 0.35), generating 10-bit I and Q data. The

FIR root raised cosine filters have an impulse response of

±4

symbols.

Transmit Calibration

When the transmit section is brought out of sleep mode

(POWER high), the transmit section initiates a self-calibration

routine to remove the offset between ITx and ITx and an offset

between QTx and QTx. READY goes high on the completion

of the self-calibration routine. Once READY goes high, BIN

(Burst In) can be brought high to initiate a transmit burst.

Ramp-Up/Down Envelope Logic

The AD7011 provides on-chip envelope shaping logic, providing

power shaping control for the beginning and end of a transmit

burst. When BIN (Burst In) is brought high, the modulator is

continues to transmit all zeros for the first three symbols, during

which the ramp-up envelope goes from zero to full scale as

illustrated in Figure 11. The next symbol to be transmitted is

–– – –– COS

π –––

1

2

1

2

t

3T

–– + –– COS

π –––

1

2

1

2

t

3T

3 SYMBOLS

3 SYMBOLS

Figure 11. Ramp Envelope

When BIN is brought low, indicating the end of a transmit

is receiving will be the last symbol to be computed for the four

symbol ramp-down sequence. Also the N

active symbol prior to ramping down.

However, because the impulse response is equal to

±4 symbols,

four additional symbols are required to fully compute the analog

outputs when transmitting the (N+4)

be eight subsequent TxCLKs, latching four additional Di-bit

CIRCUIT DESCRIPTION

TRANSMIT SECTION

The transmit section of the AD7011 generates

π/4 DQPSK I

and Q waveforms in accordance with TIA specification. This is

accomplished by a digital

π/4 DQPSK modulator, which

includes the root-raised cosine filters (

α = 0.35), followed by

two 10-bit DACs and on-chip reconstruction filters. The

π/4

DQPSK (Differential Quadrature Phase Shift Keying) digital

modulator generates 10-bit I and Q data in response to the

transmit data stream. The 10-bit I and Q DACs are filtered by

on-chip reconstruction filters, which also generate differential

analog outputs for both I and Q channels.

The AD7011 transmit channel also provides an analog mode,

where direct access to the I and Q DACs is provided, bypassing

the

π/4 DQPSK modulator. This is provided so that the

AD7011 transmit channel can also be used to perform the

conversion and filtering of the analog waveforms required to

emulate the existing analog cellular system.

/4 DQPSK Modulator

The

π/4 DQPSK modulator generates 10-bit I and Q data

(Inphase and Quadrature) which are loaded into the I and Q

10-bit transmit DACs.

Figure 9 shows the functional block diagram of the

π/4 DQPSK

modulator. The transmit serial data (TxDATA) is first con-

converter. The data is then differentially encoded; symbols are

transmitted as changes in phase rather than absolute phases.

Each symbol represents a phase change, as illustrated in Table

III, and this along with the previously transmitted symbol

determines the next symbol to be transmitted. The differential

the Di-bit symbols according to:

DIFFERENTIAL

PHASE

ENCODER

ROOT-RAISED

COSINE FILTER

I DATA

Q DATA

10

10

2-BIT

SERIAL TO

PARALLEL

CONVERTER

π /4 DQPSK DIGITAL

MODULATOR

X

k

Y

k

I

k

Q

k

ROOT-RAISED

COSINE FILTER

TxDATA

Figure 9.

π/4 DQPSK Modulator Functional Block Diagram

Table III.

∆

k

11

−3π

4

01

3

π

4

00

π

4

10

−π

4