TCM4400EPET datasheet(27/64 Pages) TI

27 / 64 page

TCM4400E

GSM/DCS BASEBAND AND VOICE A/D

AND D/A RF INTERFACE CIRCUIT

SLWS082A – JULY 1999 – REVISED MARCH 2000

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

baseband uplink path (continued)

Burst

Din

270 kHz

Differential

Encoder

Gaussian

Filter

Integrator

Power

Ramp-Up

Shaper

Cosine

Table

8-Bit

DAC

Low-Pass

Filter

Sine

Table

Low-Pass

Filter

fs = 16 x 270 kHz

8-Bit

DAC

Offset

BULIP

BULIN

BULQP

BULQN

To Power

Control DAC

Burst Timing

Control

Timing Interface

–

I/Q Gain Unbalance

Figure 7. Functional Structure of the Baseband Uplink Path

baseband downlink path

The baseband downlink path includes two identical circuits for processing the baseband I and Q components

generated by the RF circuits. The first stage of the downlink path is a continuous-time second-order antialiasing

filter (see Figure 8) that prevents aliasing due to sampling in the A/D converter. This filter also serves as an

adaptation stage (input impedance and common-mode level) between external-world and on-chip circuitry.

TYPICAL FREQUENCY RESPONSE OF THE

ANTIALIASING FILTER

–10

–20

–30

–40

–50

–60

–70

f – Frequency – Hz

102

103

104

105

106

107

Figure 8. Antialiasing Filter

TCM4400EPET Datasheet(PDF) 27 Page - Texas Instruments

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