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IDT821034 Datasheet(PDF) 4 Page - Integrated Device Technology

Part No. IDT821034
Description  QUAD PCM CODEC WITH PROGRAMMABLE GAIN
Download  19 Pages
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Maker  IDT [Integrated Device Technology]
Homepage  http://www.idt.com
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IDT821034 Datasheet(HTML) 4 Page - Integrated Device Technology

 
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4
INDUSTRIAL TEMPERATURE RANGE
IDT821034 QUAD PCM CODEC WITH PROGRAMMABLE GAIN
FUNCTIONAL DESCRIPTION
The IDT821034 contains four channel PCM CODEC with on chip digital
filters. It provides the four-wire solution for the subscriber line circuitry in
digital switches. The device converts analog voice signal into digital PCM
samples, and converts digital PCM samples back to analog signal. Digital
filters are used to bandlimit the voice signals during conversion.
The frequency of the master clock (MCLK) can be 2.048 MHz, 4.096
MHz or 8.192 MHz. Internal circuitry determines the master clock frequency
automatically.
Four channels of serial PCM data are time multiplexed via two pins, DX
and DR. The time slots of the four channels can be programmed
dynamically. The control words can be written by a microcontroller via the
Serial Control Interface. Dynamic time-slot assignment can accommodate
8 to 128 time slots corresponding to the bit clock (BCLK) frequency from
512 kHz to 8.192 MHz.
The IDT821034 offers two timing modes, delay mode and non-delay
mode. Mode selection is done by programming the Configuration Register.
The two modes are distinguished by time slot zero definition. In delay
mode, the time slot zero is defined as starting on the first rising edge of
BCLK after FS = ‘1’ is detected by the falling edge of BCLK (Figure 7).
While in non-delay mode, the time slot zero starts when both BCLK and
FS are high (Figure 8).
The device provides a programmable interface to SLIC (Subscriber Line
Interface Circuit). Each channel of the IDT821034 has three output pins
and two I/O pins for SLIC signaling. These interface pins are mapped to
internal registers and are accessed by the microcontroller via the Serial
Control Interface. In this way, the IDT821034 provides high level of
integration in line card design.
The Serial Control Interface of IDT821034 consists of four pins (CI,
CO, CS and CCLK), as shown in Figure 1, for the communication to a
microcontroller. Via this interface, the microcontroller can control the
CODEC and SLIC working modes as well as monitor the SLIC status.
OPERATION CONTROL
The following operation description applies to all four channels of the
IDT821034.
Initial State
The IDT821034 has a built-in power on reset circuit. After initial power
up, the device defaults to the following mode:
1. A-law is selected;
2. Delay mode is selected;
3. I/O pins of SLIC interface are set to input mode;
4. SLIC Control and Status Register bits are set to ‘0’;
5. All four channels are placed in standby mode;
6. All transmit and receive time slots are disabled with Time Slot Reg-
isters set to zero;
7. DX is set to high impedance state.
Operating Modes
There are two operating modes for each transmit or receive channel:
standby mode and normal mode. When the IDT821034 is first powered
on, standby mode is the default mode. Microcontroller can also set the
device into this mode via the Serial Control Interface. In standby mode, the
Serial Control Interface remains active to receive commands from the
microcontroller. All other circuits are powered down with the analog outputs
placed in high impedance state. All circuits which contain programmed
information retain the data in this mode.
Each of the four channels in the IDT821034 can be in either normal
mode or standby mode. The mode selection of each channel is done by
the microcontroller via the Serial Control Interface. When in normal mode,
each channel of the IDT821034 is able to transmit and receive both PCM
and analog information. This is the operating mode when a telephone call
is in progress.
Gain Programming
Transmit gain and receive gain of each channel in IDT821034 can be
varied by programming DSP digital filter coefficients. Transmit gain can be
varied within the range of -3 dB to +13 dB; while receive gain can be
varied within the range of -13 dB to +3 dB. This function allows the
IDT821034 to be used with SLICs of different gain requirement.
Gain programming coefficient can be written into IDT821034 via Serial
Control Interface. The detailed operation will be covered in Serial Control
Interface description. The gain programming coefficients should be
calculated as:
Transmit : Coeff_X = round [ gain_X0dB × gain_X ]
Receive: Coeff_R = round [ gain_R0dB × gain_R ]
where:
gain_X0dB = 1820;
gain_X is the target gain;
Coeff_X should be in the range of 0 to 8192.
gain_R0dB = 2506;
gain_R is the target gain;
Coeff_R should be in the range of 0 to 8192.
A gain programming coefficient is 14-bit wide and in binary format. The
7 Most Significant Bits of the coefficient is called GA_MSB_Transmit for
transmit path, or is called GA_MSB_Receive for receive path; The 7 Least
Significant Bits of the coefficient is called GA_LSB_ Transmit for transmit
path, or is called GA_LSB_Receive for receive path.
An example is given below to clarify the calculation of the coefficient. To
program a +3 dB gain in transmit path and a -3.5 dB gain in receive path:
Linear Code of +3 dB
= 103/20
= 1.412537545
Coeff_X
= round (1820 × 1.412537545)
= 2571
= 0010100, 0001011
(in binary format )
GA_MSB_Transmit
= 0010100
GA_LSB_Transmit
= 0001011
Linear Code of -3.5 dB = 10(-3.5/20)
= 0.668343917
Coeff_R
= round (2506 × 0.668343917)
= 1675
= 0001101, 0001011
(in binary format)
GA_MSB_Receive
= 0001101
GA_LSB_Receive
= 0001011


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