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IDT821064

QUAD PROGRAMMABLE PCM CODEC WITH GCI INTERFACE

Integrated Device Technology 

IDT821064 QUAD PROGRAMMABLE PCM CODEC WITH GCI INTERFACE

INDUSTRIAL TEMPERATURE RANGE

DSP PROGRAMMING

SIGNAL PROCESSING

Several blocks are programmable for signal processing. This allows

users to optimize the performance of the IDT821064 for the system.

Figure 6 shows the Signal Flow for each channel and indicate the pro-

grammable blocks.

The programmable digital filters are used to adjust gain and imped-

ance, balance transhybrid and correct frequency response. All the coef-

ficients of the digital filters can be calculated automatically by a software

provided by IDT. Users should provide accurate SLIC model, imped-

ance and gain requirements, then the software will calculate all the coef-

ficients automatically. When these coefficients are written to the coeffi-

cient RAM of the IDT82V1064, the final AC characteristics of the line

card (consists of SLIC and CODEC) will meet the ITU-T specifications.

they are: Frequency Response Correction for Transmit path (FRX) filter

and Frequency Response Correction for Receive path (FRR) filter. The

coefficients of FRX filter and FRR filter can be programmed. If the CS[4]

bit in Local Command 1 is ‘0’, the FRX coefficient is set to be default

value, while if CS[4] is ‘1’, the FRX coefficient is decided by the FRX

RAM. If the CS[6] bit in Local Command 1 is ‘0’, the FRR coefficient is

set to be default value, while if CS[6] is ‘1’, the FRR coefficient is decided

by the FRR RAM.

The address of the Coe-RAM including GTX, GRX, FRX, FRR, GIS,

ECF and IMF RAM are listed in APPENDIX.

GAIN ADJUSTMENT

The analog gain and digital gain of each channel can be adjusted

separately in IDT821064.

For each individual channel, in transmit path, analog A/D gain can be

selected as 0 dB or 6 dB. The selection is done by A/D Gain (GAD) bit in

Local Command 4. The default analog gain for transmit path is 0 dB.

For each individual channel, in receive path, analog D/A gain can be

selected as 0 dB or -6 dB. The selection is done by D/A Gain (GDA) bit

in Local Command 4. The default analog gain for receive path is 0 dB.

Digital gain of transmit path (GTX) can be programmed from -3 dB to

+12 dB with minimum 0.1 dB step. If CS[5] bit is ‘0’ in Local Command 1,

the digital gain in transmit path is set to be the default value. If CS[5] bit

is ‘1’ in Local Command 1, the digital gain in transmit path will be decided

by the coefficient in GTX RAM.

Digital gain of receive path (GRX) can be programmed from -12 dB

to +3 dB with minimum 0.1 dB step. If CS[7] bit is ‘0’ in Local Command

1, the digital gain in receive path is set to be the default value. If CS[7] bit

is ‘1’ in Local Command 1, the digital gain in receive path will be decided

by the coefficient in GRX RAM.

IMPEDANCE MATCHING

There is a programmable feedback path on each channel from VIN

to VOUT in the IDT821064. It synthesizes the two-wire impedance of the

SLIC. The Impedance Matching Filter (IMF) and the Gain of Impedance

Scaling (GIS) are adjustable, they work together to realize impedance

matching. If the CS[0] bit in Local Command 1 is ‘0’, the IMF coefficient

is set to be default value; if CS[0] is ‘0’, the IMF coefficient is set by the

IMF RAM. The CS[2] bit in Local Command 1 decides if the GIS coefficient

is programmable: if it’s ‘0’ ,the GIS coefficient is set to be default value; if

it’s ‘0’, the GIS coefficient is set by the GIS RAM.

TRANSHYBRID BALANCE

Transhybrid balancing filter is used to adjust transhybrid balance to

ensure the echo cancellation meets the ITU-T specifications. The coef-

ficient for Echo Cancellation (ECF) can be programmed. If the CS[1] bit

in Local Command 1 is ‘0’, the coefficient of ECF is set to be default

value; if CS[1] is ‘1’, the coefficient of ECF is decided by the ECF RAM.

FREQUENCY RESPONSE CORRECTION

The IDT821064 provides two filters that can be programmed to cor-

rect any frequency distortion caused by the impedance matching filter,

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