LE58QL022BVC datasheet(31/61 Pages) ZARLINK

31 / 61 page

Le58QL022

Data Sheet

Zarlink Semiconductor Inc.

SIGNAL PROCESSING

Overview of Digital Filters

Several of the blocks in the signal processing section are user programmable. These allow the user to optimize the performance

of the QLSLAC device for the system. Figure 20 shows the QLSLAC device signal processing and indicates the programmable

blocks.

The advantages of digital filters are:

High reliability

No drift with time or temperature

Unit-to-unit repeatability

Superior transmission performance

Flexibility

Maximum possible bandwidth for V.90 modems

Figure 20.

QLSLAC Transmission Block Diagram

Two-Wire Impedance Matching

Two feedback paths on the QLSLAC device synthesize the two-wire input impedance of the SLIC by providing a programmable

feedback path from VIN to VOUT. The Analog Impedance Scaling Network (AISN) is a programmable analog gain of

−0.9375 • GIN to +0.9375 • GIN from V

IN to VOUT. (See GIN in Electrical Characteristics, on page 10.) The Z filter is a

programmable digital filter providing an additional path and programming flexibility over the AISN in modifying the transfer

function from VIN to VOUT. Together, the AISN and the Z-Filter enable the user to synthesize virtually all required SLIC input

impedances.

Frequency Response Correction and Equalization

The QLSLAC device contains programmable filters in the receive (R) and transmit (X) directions that may be programmed for

line equalization and to correct any attenuation distortion caused by the Z filter.

Transhybrid Balancing

The QLSLAC device’s programmable B filter is used to adjust transhybrid balance. The filter has a single pole IIR section (BIIR)

and an eight-tap FIR section (BFIR), both operating at 16 kHz. (See commands 86/87h and 96/97h.)

GIN

AISN

ADC

DAC

Inter-

polator

Deci-

mator

Deci-

mator

Inter-

polator

LPF &

HPF

LPF

Ex-

pander

TSA

Com-

pressor

High Pass Filter (HPF)

Full

Digital

Loopback

(FDL)

OUT

VREF

Lower Receive

Gain (LRG)

Cutoff Receive

Path (CRP)

TSA Loopback

(TLB)

Cutoff

Transmit

Path

(CTP)

Digital

1 kHz Tone

(TON)

* programmable blocks

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