MITEL MT9122AE, MT9122AP Datasheet

CMOS

MT9122

Dual Voice Echo Canceller

Preliminary Information

Features

• Dual channel 64ms or single channel 128ms echo cancellation

• Conforms to ITU-T G.165 requirements

• ITU-T G.165/G.164 disable tone detection supported on all audio paths

• Narrow-band signal detection

• Programmable double-talk detection threshold

• Non-linear processor with adaptive suppression threshold and comfort noise insertion

• Offset nulling of all PCM channels

• Controllerless mode or Controller mode with serial interface

• ST-BUS or variable-rate SSI PCM interfaces

• Selectable µ/A-Law ITU-T G.711; µ/A-Law Sign Mag; linear 2’s complement

• Per channel selectable 12 dB attenuator

• Transparent data transfer and mute option

• 19.2 MHz master clock operation

Applications

with Tone Detection

ISSUE 5 September 1996

Ordering Information

MT9122AP 28 Pin PLCC MT9122AE 28 Pin PDIP

-40 °C to + 85 °C

Description

The MT9122 Voice Echo Canceller implements a cost effective solution for telephony voice-band echo cancellation conforming to ITU-T G.165 requirements. The MT9122 architecture contains two echo cancellers which can be conﬁgured to provide dual channel 64 millisecond echo cancellation or single channel 128 millisecond echo cancellation. The MT9122 supports ITU-T G.165 or G.164 tone disable requirements.

The MT9122 operates in two major modes: Controller or Controllerless. Controller mode allows access to an array of features for customizing the MT9122 operation. Controllerless mode is for applications where default register settings are sufﬁcient.

• Wireless Telephony

• Trunk echo cancellers

Sin

Rout

ENA2 ENB2

NLP REV LAW

FORMAT

TD1

TD2

µ/A-Law

Programmable Bypass

Linear/

Disable Tone

Detector

Offset

Null

Linear/

µ/A-Law

Adaptive

Echo Canceller A

Non-Linear

Processor

Filter

Control

Narrow-Band

Detector

12dB

Attenuator

Echo Canceller B

Linear/

µ/A-Law

Microprocessor

Interface

Double-Talk

Detector

Offset

Null

Disable Tone

Detector

Linear/

µ/A-Law

Sout

Rin ENA1 ENB1

CONFIG1 CONFIG2 S1/DATA1 S2/DATA2

S3/ S4/SCLK

VDD VSS PWRDN IC F0od F0i BCLK/C4i MCLK

Figure 1 - Functional Block Diagram

8-17

MT9122 Preliminary Information

ENA1 ENB1 ENA2 ENB2

Rin Sin

VSS

MCLK

NLP REV LAW

FORMAT

PWRDN

1 2

3 4 5

PDIP

6 7 8 9

10 11 12 13 14

28 27 26 25 24 23 22 21 20 19 18 17 16 15

CONFIG2 CONFIG1

BCLK/

C4i

F0i Rout

Sout VDD

F0od S1/DATA1 S2/DATA2 S3/

CS S4/SCLK TD1 TD2

Rin Sin

VSS

MCLK

NLP

REV

ENB2

ENB1

ENA1

ENA2

LAW

PLCC

PWRDN

FORMAT

•

5 6 7 8 9

10 11

CONFIG2

TD2

TD1

BCLK/C4i

CONFIG1

25 24 23 22 21 20 19

CS S3/

S4/SCLK

F0i Rout Sout VDD F0od S1/DATA1 S2/DATA2

Figure 2 - Pin Connections

Pin Description

Pin # Name Description

1 ENA1 SSI Enable Strobe / ST-BUS Mode for Rin/Sout (Input). This pin has dual functions

depending on whether SSI or ST-BUS is selected. For SSI, this strobe must be present f or fr ame synchronization. This is an active high channel

enable strobe, 8 or 16 data bits wide, enabling serial PCM data transfer for Echo Canceller A on Rin/Sout pins. Strobe period is 125 microseconds.

For ST-BUS, this pin, in conjunction with the ENB1 pin, will select the proper ST-BUS mode f or Rin/Sout pins (see ST-BUS Operation description). The selected mode applies to both Echo Canceller A and B.

2 ENB1 SSI Enable Strobe / ST-BUS Mode for Rin/Sout (Input).This pin has dual functions

depending on whether SSI or ST-BUS is selected. For SSI, this is an active high channel enable strobe, 8 or 16 data bits wide, enabling serial

PCM data transfer f orEcho Canceller B on Rin/Sout pins . Strobe period is 125 microseconds. For ST-BUS, this pin, in conjunction with the ENA1 pin, will select the proper ST-BUS mode f or

Rin/Sout pins (see ST-BUS Operation description). The selected mode applies to both Echo Canceller A and B.

3 ENA2 SSI Enable Strobe / ST-BUS Mode for Sin/Rout (Input).This pin has dual functions

depending on whether SSI or ST-BUS is selected. For SSI, this is an active high channel enable strobe, 8 or 16 data bits wide, enabling serial

PCM data transfer f orEcho Canceller A on Sin/Rout pins . Strobe period is 125 microseconds. For ST-BUS, this pin, in conjunction with the ENB2 pin, will select the proper ST-BUS mode f or

Sin/Rout pins (see ST-BUS Operation description). The selected mode applies to both Echo Canceller A and B.

4 ENB2 SSI Enable Strobe / ST-BUS Mode for Sin/Rout (Input).This pin has dual functions

depending on whether SSI or ST-BUS is selected. For SSI, this is an active high channel enable strobe, 8 or 16 data bits wide, enabling serial

PCM data transfer f orEcho Canceller B on Sin/Rout pins . Strobe period is 125 microseconds.

8-18

For ST-BUS, this pin, in conjunction with the ENA2 pin, will select the proper ST-BUS mode f or Sin/Rout pins (see ST-BUS Operation description). The selected mode applies to both Echo Canceller A and B.

Preliminary Information MT9122

Pin Description (continued)

Pin # Name Description

5 Rin Receive PCM Signal Input (Input). 128 kbit/s to 4096 kbit/s serial PCM input stream. Data

may be in either companded or 2’s complement linear format. Two PCM channels are timemultiplexed on this pin. These are the Receive Input reference channels for Echo Cancellers A and B. Data bits are clocked in following SSI or ST-BUS timing requirements.

6 Sin Send PCM Signal Input (Input). 128 kbit/s to 4096 kbit/s serial PCM input stream. Data

may be in either companded or 2’s complement linear format. Two PCM channels are timemultiplexed on this pin. These are the Send Input channels (after echo path) for Echo Cancellers A and B. Data bits are clocked in following SSI or ST-BUS timing requirements.

7 VSS Digital Ground: Nominally 0 volts. 8 MCLK Master Clock (Input): Nominal 20 MHz Master Clock input. May be connected to an

asynchronous (relative to frame signal) clock source.

9 IC Internal Connection (Input): Must be tied to Vss.

10 NLP Non-Linear Processor Control (Input):

Controllerless Mode: An active high enables the Non-Linear Processors in Echo Cancellers A and B. Both NLP’ s are disab led when lo w. Intended for conformance testing to G.165 and it is usually tied to Vdd for normal operation.

Controller Mode: This pin is ignored (tie to Vdd or Vss). The non-linear processor operation is controlled by the NLPDis bit in Control Register 2. Refer to the Register Summary.

11 REV Reversal Detection (Input):

Controllerless Mode: An active high conﬁgures all the tone detectors to trigger only when a 2100Hz disable tone with periodic phase reversal is present (per G.165). When low, the tone detectors will trigger upon detection of any 2100Hz disable tone, with or without periodic phase reversal (per G.164).

Controller Mode: This pin is ignored (tie to VDD or VSS). The operation is controlled by the PHDis bit in Control Register 2. Refer to the Register Summary.

12 LAW A/µ Law Select (Input):

An active low selects µ−Law companded PCM. When high, selects A-Law companded PCM. This control is for both echo cancellers and is valid for both controller and controllerless modes.

13 FORMAT ITU-T/Sign Mag (Input):

An active low selects sign-magnitude PCM code. When high, selects ITU-T (G.711) PCM code. This control is for both echo cancellers and is v alid f or both controller and controllerless modes.

14 PWRDN Power-down (Input): An active low resets the device and puts the MT9122 into a low-power

stand-by mode.

15 TD2 Tone Detect 2 (Output):

An active low output occurs when Echo Canceller B detects the presence of a valid 2100Hz disabling tone (G.164 or G.165) on Rin or Sin pins. This output returns to a logic high once the release criteria are met. The behavior of this pin is identical in both controller and controllerless modes.

16 TD1 Tone Detect 1 (Output):

An active low output occurs when Echo Canceller A detects the presence of a valid 2100Hz disabling tone (G.164 or G.165) on Rin or Sin pins. This output returns to a logic high once the release criteria are met. The behavior of this pin is identical in both controller and controllerless modes.

8-19

MT9122 Preliminary Information

Pin Description (continued)

Pin # Name Description 17/18

S4/S3

Selection of Echo Canceller B Functional States (Input):

Controllerless Mode: Selects Echo Canceller B functional states according to Table 2. Controller Mode: S4 and S3 pins become SCLK and CS pins respectively.

17 18

19/20

SCLK

S2/S1

Serial Port Synchronous Clock (Input): Data clock for the serial microport interface. Chip Select (Input): Enables serial microport interface data transfers. Active low.

Selection of Echo Canceller A Functional States (Input):

Controllerless Mode: Selects Echo Canceller A functional states according to Table 2. Controller Mode: S2 and S1 pins become DATA2 and DATA1 pins respectively.

DATA2

Serial Data Receive (Input):

In Motorola/National serial microport operation, the DATA2 pin is used for receiving data. In Intel serial microport operation, the DATA2 pin is not used and must be tied to Vss or Vdd.

DATA1

Serial Data Port (Bidirectional):

In Motorola/National serial microport operation, the DAT A1 pin is used f or tr ansmitting data. In Intel serial microport operation, the DATA1 pin is used for transmitting and receiving data.

21 F0od Delayed Frame Pulse Output (Output):

In ST-BUS operation, this pin generates a delay ed frame pulse after the 4th channel time slot and is used for daisy-chaining multiple ST-BUS devices. See Figures 5 to 8.

In SSI operation, this pin outputs logic low.

22 VDD Positive Power Supply: Nominally 5 volts. 23 Sout Send PCM Signal Output (Output):

128 kbit/s to 4096 kbit/s serial PCM output stream. Data may be in either companded or 2’s complement linear PCM format. Two PCM channels are time-multiplexed on this pin. These are the Send Out signals after echo cancellation and Non-linear processing. Data bits are clocked out following SSI or ST-BUS timing requirements.

24 Rout Receive PCM Signal Output (Output):

128 kbit/s to 4096 kbit/s serial PCM output stream. Data may be in either companded or 2’s complement linear PCM format. Two PCM channels are time-multiplexed on this pin. This output pin is provided for convenience in some applications and may not always be required. Data bits are clocked out following SSI or ST-BUS timing requirements.

25 F0i Frame Pulse (input):

In ST-BUS operation, this is a frame alignment low going pulse. SSI operation is enabled by connecting this pin to Vss.

26 BCLK/C4i Bit Clock/ST-BUS Clock (Input):

In SSI operation, BCLK pin is a 128 kHz to 4.096 MHz bit clock. This clock must be synchronous with ENA1, ENA2, ENB1 and ENB2 enable strobes.

In ST-BUS operation, C4i pin must be connected to the 4.096MHz (C4) system clock.

27/28 CONFIG1/

CONFIG2

Device Conﬁguration Pins (Inputs).

When CONFIG1 and CONFIG2 pins are both logic 0, the MT9122 serial microport is enabled. This conﬁguration is deﬁned as Controller Mode. When CONFIG1 and CONFIG2 pins are in any other logic combination, the MT9122 is conﬁgured in Controllerless Mode. See Table 3.

Notes:

1. All un used inputs should be connected to logic lo w or high unless otherwise stated. All outputs should be left open circuit when not used.

2. All inputs have TTL compatible logic levels except for MCLK, Sin and Rin pins which have CMOS compatible logic levels and PWRDN pin which has Schmitt trigger compatible logic levels.

3. All outputs are CMOS pins with CMOS logic levels.

8-20

Preliminary Information MT9122

Functional Description

The MT9122 architecture contains two individually controlled echo cancellers (Echo Canceller A and B). They can be set in three distinct conﬁgurations: Normal, Back-to-Back and Extended Delay (see Figure 3). Under Normal conﬁguration, the two echo cancellers are positioned in parallel providing 64 millisecond echo cancellation in two channels simultaneously. In Back-to-Back conﬁguration, the two echo cancellers are positioned to cancel echo coming from both directions in a single channel. In Extended-Delay conﬁguration, the two echo cancellers are internally cascaded into one 128 millisecond echo canceller.

Each echo canceller contains the following main elements (see Figure 1).

• Adaptive Filter for estimating the echo channel

• Subtracter for cancelling the echo

• Double-Talk detector for disabling the ﬁlter adaptation during periods of double-talk

• Non-Linear Processor for suppression of residual echo

• Disable Tone Detectors for detecting valid disable tones at the input of receive and send paths

• Narrow-Band Detector for preventing Adaptive Filter divergence caused by narrow-band signals

• Offset Null ﬁlters for removing the DC component in PCM channels

• 12dB attenuator for signal attenuation

• Serial controller interface compatible with Motorola, National and Intel microcontrollers

• PCM encoder/decoder compatible with µ/ALaw ITU-T G.711, µ/A-Law Sign-Mag or linear 2’s complement coding

The MT9122 has two modes of operation:

Controllerless

and

Controller

. Controllerless mode is intended for applications where customization is not required. Controller mode allows access to all registers for customizing the MT9122 operation. Refer to Table 7 for a complete list. Controller mode is selected when CONFIG1 and CONFIG2 pins are both connected to Vss.

Each echo canceller in the MT9122 has four functional states: and

Enable Adaptation

Mute,Bypass,Disable Adaptation

. These are explained in the

section entitled Echo Canceller Functional States.

Sin

echo path A

Rout

echo path B

PORT 2

channel A

E.C.A

channel B

E.C.B

Adaptive

Filter (64ms)

Optional -12dB pad

Adaptive

Filter (64ms)

Optional -12dB pad

a) Normal Conﬁguration (64ms)

PORT 1

Sout

Rin

PORT 2

echo

path A

Rout

Sin

channel A

E.C.A

Adaptive Filter

(128 ms)

Optional -12dB pad

PORT 1

b) Extended Delay Conﬁguration (128ms)

PORT 2

Sin

echo path

Rout Rin

Optional -12dB pad

Adaptive

Filter (64ms)

E.C.A

Filter (64ms)

Optional -12dB pad

Adaptive

E.C.B

PORT 1

echo path

c) Back-to-Back Conﬁguration (64ms)

Sout

Rin

Sout

Figure 3 - Device Conﬁguration

8-21

MT9122 Preliminary Information

Adaptive Filter

The adaptive ﬁlter is a 1024 tap FIR ﬁlter which is divided into two sections. Each section contains 512 taps providing 64ms of echo estimation. In Normal conﬁguration, the ﬁrst section is dedicated to channel A and the second section to channel B. In Extended Delay conﬁguration, both sections are cascaded to provide 128ms of echo estimation in channel A.

Double-Talk Detector

Double-Talk is deﬁned as those periods of time when signal energy is present in both directions simultaneously. When this happens, it is necessary to disable the ﬁlter adaptation to prevent divergence of the adaptive ﬁlter coefﬁcients. Note that when double-talk is detected, the adaptation process is halted but the echo canceller continues to cancel echo.

A double-talk condition exists whenever the Sin signal level is greater than the expected retur n echo level. The relative signal levels of Rin (Lrin) and Sin (Lsin) are compared according to the following expression to identify a double-talk condition:

The DTDT register is 16 bits wide. The register value in hexadecimal can be calculated with the following equation:

DTDT

where 0 < DTDT

= hex(DTDT

(hex)

< 1

(dec)

* 32768)

Example: For DTDT = 0.5625 (-5dB), the

hexadecimal value becomes

hex(

0.5625 * 32768) = 4800h

Non-Linear Processor (NLP)

After echo cancellation, there is always a small amount of residual echo which may still be audible. The MT9122 uses an NLP to remove residual echo signals which have a level lower than the Adaptive Suppression Threshold (TSUP in G.165). This threshold depends upon the level of the Rin (Lrin) reference signal as well as the programmed value of the Non-Linear Processor Threshold register (NLPTHR). TSUP can be calculated by the following equation:

TSUP = Lrin + 20log10(NLPTHR)

Lsin > Lrin + 20log10(DTDT)

where DTDT is the Double-Talk Detection Threshold. Lsin and Lrin are the relative signal levels expressed in dBm0.

A different method is used when it is uncertain whether Sin consists of a low level double-talk signal or an echo return. During these periods, the adaptation process is slowed down but it is not halted.

Controllerless Mode

In G.165 standard, the echo return loss is expected to be at least 6dB. This implies that the Double-Talk Detector Threshold (DTDT) should be set to 0.5 (-6dB). However, in order to get additional guardband, the DTDT is set internally to 0.5625 (-5dB). In controllerless mode, the Double-Talk Detector is always active.

Controller Mode

In some applications the return loss can be higher or lower than 6dB. The MT9122 allows the user to change the detection threshold to suit each application’s need. This threshold can be set by writing the desired threshold value into the DTDT register.

where NLPTHR is the Non-Linear Processor Threshold register value and Lrin is the relative power level expressed in dBm0.

When the level of residual error signal falls below TSUP, the NLP is activated further attenuating the residual signal to less than -65dBm0. To prevent a perceived decrease in background noise due to the activation of the NLP, a spectrally-shaped comfort noise, equivalent in power level to the background noise, is injected. This keeps the perceived noise level constant. Consequently, the user does not hear the activation and de-activation of the NLP.

Controllerless Mode

The NLP processor can be disabled by connecting the NLP pin to Vss.

Controller Mode

The NLP processor can be disabled by setting the NLPDis bit to 1 in Control Register 2.

The NLPTHR register is 16 bits wide. The register value in hexadecimal can be calculated with the following equation:

NLPTHR

= hex(NLPTHR

(hex)

(dec)

* 32768)

8-22

Preliminary Information MT9122

where 0 < NLPTHR

(dec)

< 1

The comfort noise injection can be disabled by setting the INJDis bit to 1 in Control Register 1.

It should be noted that the NLPTHR is valid and the comfort noise injection is active only when the NLP is enabled.

Disable Tone Detector

G.165 recommendation deﬁnes the disable tone as having the following characteristics: 2100 Hz (± 21Hz) sinewave, a power level between -6 to

-31dBm0, and a phase reversal of 180 degrees (±25 degrees) every 450ms (±24ms). If the disable tone is present for a minimum of one second with at least one phase reversal, the Tone Detector will tr igger.

G.164 recommendation deﬁnes the disable tone as a 2100 Hz (±21Hz) sinewave with a power level between -6 to -31dBm0. If the disable tone is present for a minimum of one second, with or without phase reversal, the Tone Detector will tr igger.

The MT9122 has four Tone Detectors in order to monitor the occurrence of a valid disable tone on channels A and B on both Rin and Sin. Upon detection of a disable tone, output pins TD1 or TD2 will go low as illustrated in Figure 4.

Rin

Tone Detector

TD1

Sin

Tone Detector

Controllerless Mode

The selection between G.165 and G.164 tone disable is controlled by the REV pin. When the REV pin is connected to Vss, G.164 is selected. This applies to all four Tone Detectors.

In response to a valid disable tone, the MT9122 must be switched from the Enable Adaptation state to the Bypass state. In an application, the Tone Detect outputs, TD1 and TD2, may be used to switch the echo cancellers between these two states. This is achieved by connecting S1 and S3 pins to Vdd and by connecting the TD1 and TD2 outputs to the S2 and S4 input pins respectively.

Controller Mode

The selection between G.165 and G.164 tone disable is controlled by the PHDis bit in Control Register 2. When the PHDis bit is set to 1, G.164 tone disable requirements are selected. This applies to all four Tone Detectors.

In response to a valid disable tone, the MT9122 must be switched from the Enable Adaptation state to the Bypass state. This can be done in two ways, automatically or externally. In automatic mode, the Tone Detectors internally control the switching between Enable Adaptation and Bypass states. The automatic mode can be activated by setting the AutoTD bit in Control Register 2 to high. In external mode, an external controller is needed to poll the TD bit in Status Register A or B. Following the detection of a disable tone (TD bit high), the external controller should switch the echo canceller from Enable Adaptation to Bypass state.

Echo Canceller A

Rin

Tone Detector

TD2

Sin

Tone Detector

Echo Canceller B

Figure 4 - Disable Tone Detection

Once a Tone Detector has been triggered, the MT9122 no longer needs a valid disable tone (G.164 or G.165) to maintain Tone Detector status (e.g. TD1, TD2 pins low). The Tone Detector status will only release (e.g. TD1, TD2 pins high) if the signals Rin and Sin fall below -30dBm0, in the frequency range of 390Hz to 700Hz, and below -34dBm0, in the frequency range of 700Hz to 3400Hz, for at least 400ms.

TD1 and TD2 output pins remain active, as in

The Controllerless mode, and they can be used as an interrupt to an external controller.

Narrow Band Signal Detector (NBSD)

Single or dual frequency tones (e.g. DTMF tones) present in the reference input (Rin) of the echo canceller for a prolonged period of time may cause the adaptive ﬁlter to diverge. The Narrow Band Signal Detector (NBSD) is designed to prevent this divergence by detecting single or dual tones of arbitrary frequency, phase, and amplitude. When narrow band signals are detected, the adaptation process is halted but the echo canceller continues to cancel echo.

8-23

MT9122 Preliminary Information

Controllerless Mode

The NBSD is always active and automatically disables the ﬁlter adaptation process when narrow band signals are detected.

Controller Mode

The NBSD can be disabled by setting the NBDis bit to 1 in Control Register 2.

Offset Null Filter

Adaptive ﬁlters in general do not operate properly when a DC offset is present on either the reference signal (Rin) or the echo composite signal (Sin). To remove the DC component, the MT9122 incorporates Offset Null ﬁlters in both Rin and Sin inputs.

Controllerless Mode

The Offset Null ﬁlters are always active.

Controller Mode

The offset null ﬁlters can be disabled by setting the HPFDis bit to 1 in Control Register 2.

Echo Canceller Functional States

canceller. In this conﬁguration, muting Echo Canceller A causes quiet code to be transmitted on Rout.

Bypass: The Bypass state directly transfers PCM codes from

Rin to Rout and from Sin to Sout. When Bypass state is selected, the adaptive ﬁlter coefﬁcients are reset to zero.

Disable Adaptation: When the Disable Adaptation state is selected, the

adaptive ﬁlter coefﬁcients are frozen at their current value. In this state, the adaptation process is halted however the MT9122 continues to cancel echo.

Enable Adaptation: In Enable Adaptation state, the adaptive ﬁlter

coefﬁcients are continually updated. This allows the echo canceller to model the echo return path characteristics in order to cancel echo. This is the normal operating state.

Controllerless Mode

The four functional states can be selected via S1, S2, S3, and S4 pins as shown in the following table.

Each echo canceller has four functional states: Mute, Bypass, Disable Adaptation and Enable Adaptation.

Mute: The Mute state forces the echo canceller to

transmit quiet code and halts the ﬁlter adaptation process.

In Normal conﬁguration, the PCM output data on Rout is replaced with the quiet code according to the following table.

+Zero

(quiet code)

LINEAR

16 bits

2’s

complement

0000h 80h FFh D5h

SIGN/

MAGNITUDE

µ-Law

A-Law

CCITT (G.711)

µ-Law A-Law

Table 1 - Quiet PCM Code Assignment

In Back-to-Back conﬁguration, both echo cancellers are combined to implement a full duplex echo canceller. Therefore muting Echo Canceller A causes quiet code to be transmitted on Rout, while muting Echo Canceller B causes quiet code to be transmitted on Sout.

In Extended Delay conﬁguration, both echo cancellers are cascaded to make one 128ms echo

Echo

Canceller A

S2/S1

00 Mute 01 Bypass 10 Disable Adaptation 11 Enable Adaptation

(1) Filter coefficients are frozen (adaptation disabled) (2) The adaptive filter coefficients are reset to zero (3) The MT9122 cancels echo

Functional State

(1)

(2)

(1,3)

(3)

Echo

Canceller B

S4/S3

00 01 10 11

Table 2 - Functional States Control Pins

Controller Mode

The echo canceller functions are selected in Control Register 1 and Control Register 2 through four control bits: MuteS, MuteR, Bypass and AdaptDis. See Register Summary for details.

MT9122 Throughput Delay

The throughput delay of the MT9122 varies according to the data path and the device conﬁguration. For all device conﬁgurations, except for Bypass state, Rin to Rout has a delay of two frames and Sin to Sout has a delay of three frames.

8-24

Preliminary Information MT9122

In Bypass state, the Rin to Rout and Sin to Sout paths have a delay of two frames. In ST-BUS operation, the D and C channels have a delay of one frame.

Power Down

Forcing the PWRDN pin to logic low, will put the MT9122 into a power down state. In this state all internal clocks are halted, the DATA1, Sout and Rout pins are tristated and the F0od, TD1, and TD2 pins output high.

The device will automatically begin the execution of its initialization routines when the PWRDN pin is returned to logic high and a clock is applied to the MCLK pin. The initialization routines execute for one frame and will set the MT9122 to default register values.

Device Conﬁguration

The MT9122 architecture contains two individually controlled echo cancellers (Echo Canceller A and B). They can be set in three distinct conﬁgurations: Normal, Back-to-Back, and Extended Delay. See Figure 3.

In SSI operation, ENA1 and ENA2 enable pins are used to strobe data on Rin/Sout and Sin/Rout respectively. In ST-BUS operation, ENA1, ENA2, ENB1 and ENB2 inputs are used to select the STBUS mode according to Table 4.

Examples of Back-to-Back conﬁguration include positioning the MT9122 between a codec and a transmission device or between two codecs for echo control on analog trunks.

Extended Delay conﬁguration: In this conﬁguration, the two echo cancellers are

internally cascaded into one 128 millisecond echo canceller. See Figure 3b. In SSI operation, ENA1 and ENA2 enable pins are used to strobe data on Rin/Sout and Sin/Rout respectively. In ST-BUS operation, ENA1, ENA2, ENB1 and ENB2 inputs are used to select the ST-BUS mode according to Table

Controllerless Mode

The three conﬁgurations can be selected through the CONFIG1 and CONFIG2 pins as shown in the following table.

CONFIG1 CONFIG2 CONFIGURATION

Normal Conﬁguration: In this conﬁguration, the two echo cancellers (Echo

Canceller A and B) are positioned in parallel, as shown in Figure 3a, providing 64 milliseconds of echo cancellation in two channels simultaneously.

In SSI operation, both channels are available in different timeslots on the same TDM (Time Division Multiplexing) bus. For Echo Canceller A, the ENA1 enable strobe pin deﬁnes the Rin/Sout (PORT1) time slot while the ENA2 enable strobe pin deﬁnes the Sin/Rout (PORT2) time slot. The ENB1 and ENB2 enable strobes perform the same function for Echo Canceller B.

In ST-BUS operation, the ENA1, ENA2, ENB1 and ENB2 pins are used to determine the PCM data format and the channel locations. See Table 4.

Back-to-Back Conﬁguration: In this conﬁguration, the two echo cancellers are

positioned to cancel echo coming from both directions in a single channel providing full duplex 64 millisecond echo-cancellation. See Figure 3c. This conﬁguration uses only one timeslot on PORT1 and PORT2, allowing a no-glue interface for applications where bidirectional echo cancellation is required.

00 0 1 Extended Delay Mode 1 0 Back-to-Back Mode 1 1 Normal Mode

(selects Controller Mode)

Table 3 - Conﬁguration in Controllerless Mode

Controller Mode

In Control Register 1, the Normal conﬁguration can be programmed by setting both BBM and ExtendedDelay bits to 0. Back-to-Back conﬁguration can be programmed by setting the BBM bit to 1 and Extended-Delay bit to 0. Extended-Delay conﬁguration can be programmed by setting the Extended-Delay bit to 1 and BBM bit to 0. Both BBM and Extended-Delay bits in Control Register 1 can not be set to 1 at the same time.

PCM Data I/O

The PCM data transfer for the MT9122 is provided through two PCM ports. PORT1 consists of Rin and Sout pins while PORT2 consists of Sin and Rout Pins. The Data is transferred through these ports according to either ST-BUS or SSI conventions. The device determines the mode of operation by monitoring the signal applied to the

F0i pin. When a

8-25

MT9122 Preliminary Information

valid ST-BUS frame pulse is applied to the F0i pin, the MT9122 will assume ST-BUS operation. If F0i is tied continuously to Vss the MT9122 will assume SSI operation.

ST-BUS Operation

The ST-BUS PCM interface conforms to Mitel’s STBUS standard and it is used to transport 8 bit companded PCM data (using one timeslot) or 16 bit 2’s complement linear PCM data (using two timeslots). Pins ENA1 and ENB1 select timeslots on PORT1 while pins ENA2 and ENB2 select timeslots on PORT2. See Table 4 and Figures 5 to 8.

PORT1

Rin/Sout

Enable Pins Enable Pins

ENB1 ENA1 ENB2 ENA2

00Mode 1. 8 bit companded PCM I/O on

timeslots 0 & 1.

01Mode 2. 8 bit companded PCM I/O on

timeslots 2 & 3.

10Mode 3. 8 bit companded PCM I/O on

timeslots 2 & 3. Includes D & C channel bypass in timeslots 0 & 1.

11Mode 4. 16 bit 2’s complement linear

PCM I/O on timeslots 0 - 3.

ST-BUS Mode

Selection

PORT2

Sin/Rout

and ENB2) are used for parsing input/output data and they must pulse within 125 microseconds of the rising edge of ENA1. If they are unused, they must be tied to Vss.

In SSI operation, the enable strobes may be a mixed combination of 8 or 16 BCLK cycles allowing the ﬂexibility to mix 2’s complement linear data on one port (e.g., Rin/Sout) with companded data on the other port (e.g., Sin/Rout).

Enable Strobe Pin Echo Canceller Port

ENA1 A 1 ENB1 B 1 ENA2 A 2 ENB2 B 2

Table 5 - SSI Enable Strobe Pins

PCM Law and Format Control (LAW, FORMAT)

The PCM companding/coding law used by the MT9122 is controlled through the LAW and FORMAT pins. ITU-T G.711 companding curves for µ-Law and A-Law are selected by the LAW pin. PCM coding ITU-T G.711 and Sign-Magnitude are selected by the FORMAT pin. See Table 6.

Table 4 - ST-BUS Mode Select

Note that if the device is in back-to-back or extended delay conﬁgurations, the second timeslot in any STBUS Mode contains undeﬁned data. This means that the following timeslots contain undeﬁned data: timeslot 1 in ST-BUS Mode 1; timeslot 3 in ST-BUS Modes 2 & 3 and timeslots 2 and 3 in ST-BUS Mode

SSI Operation

The SSI PCM interface consists of data input pins (Rin, Sin), data output pins (Sout, Rout), a variable rate bit clock (BCLK), and four enable pins (ENA1,ENB1, ENA2 and ENB2) to provide strobes for data transfers. The active high enable may be either 8 or 16 BCLK cycles in duration. Automatic detection of the data type (8 bit companded or 16 bit 2’s complement linear) is accomplished internally. The data type cannot change dynamically from one frame to the next.

In SSI operation, the frame boundary is determined by the rising edge of the ENA1 enable strobe (see Figure 9). The other enable strobes (ENB1, ENA2

Sign-Magnitude

FORMAT=0

PCM Code

µ/A-LAW

LAW = 0 or 1

+ Full Scale 1111 1111 1000 0000 1010 1010

+ Zero 1000 0000 1111 1111 1101 0101

- Zero 0000 0000 0111 1111 0101 0101

- Full Scale 0111 1111 0000 0000 0010 1010

ITU-T (G.711)

FORMAT=1

µ-LAW

LAW = 0

A-LAW

LAW =1

Table 6 - Companded PCM

Linear PCM

The 16-bit 2’s complement PCM linear coding permits a dynamic range beyond that which is speciﬁed in ITU-T G.711 for companded PCM. The echo-cancellation algorithm will accept 16 bits 2’s complement linear code which gives a dynamic range of +15dBm0. Note however that the tone detectors must be limited to the maximum dynamic range speciﬁed in G.711 (+3.14 or +3.17 dBm0).

8-26

+ 22 hidden pages