MITEL MT88E45AS Datasheet

MT88E45

4-Wire Calling Number Identiﬁcation Circuit 2

Advance Information

Features

• Compatible with:

• Bellcore GR-30-CORE, SR-TSV-002476, ANSI/TIA/EIA-716, draft TIA/EIA-777;

• ETSI ETS 300 778-1 (FSK only variant) & -2;

• BT (British Telecom) SIN227 & SIN242

• Bellcore ‘CPE Alerting Signal’ (CAS), ETSI ‘Dual Tone Alerting Signal’ (DT-AS), BT Idle State and Loop State ‘Tone Alert Signal’ detection

• 1200 baud Bell 202 and CCITT V.23 FSK demodulation

• Separate differential input ampliﬁers with adjustable gain for Tip/Ring and telephone hybrid or speech IC connections

• Selectable 3-wire FSK data interface (bit stream or 1 byte buffer)

• Facility to monitor the stop bit for framing error check

• FSK Carrier detect status output

• 3 to 5V +/- 10% supply voltage

• Uses 3.579545MHz crystal or ceramic resonator

• Low power CMOS with power down

Applications

• Bellcore CID (Calling Identity Delivery) and CIDCW (Calling Identity Delivery on Call Waiting) telephones and adjuncts

• ETSI, BT CLIP (Calling Line Identity Presentation) and CLIP with Call Waiting telephones and adjuncts

• Fax and answering machines

• Computer Telephony Integration (CTI) systems

(4-Wire CNIC2)

DS5143 ISSUE 2 March 1999

Ordering Information

MT88E45AS 20 Pin SOIC

-40°C to 85°C

Description

The MT88E45 is a low power CMOS integrated circuit suitable for receiving the physical layer signals used in North American (Bellcore) Calling Identity Delivery on Call Waiting (CIDCW) and Calling Identity Delivery (CID) services. It is also suitable for ETSI and BT Calling Line Identity Presentation (CLIP) and CLIP with Call Waiting services.

The MT88E45 contains a 1200 baud Bell 202/CCITT V.23 FSK demodulator and a CAS/DT-AS detector. Two input op-amps allow the MT88E45 to be connected to both Tip/Ring and the telephone hybrid or speech IC receive pair for optimal CIDCW telephone architectural implementation. FSK demodulation is always on Tip/Ring, while CAS detection can be on Tip/Ring or Hybrid Receive. Tip/ Ring CAS detection is required for Bellcore’s proposed Multiple Extension Interworking (MEI) and BT’s on-hook CLIP. A selectable FSK data interface allows the data to be processed as a bit stream or extracted from a 1 byte on chip buffer. Power management has been incorporated to power down the FSK or CAS section when not required. Full chip power down is also available. The MT88E45 is suitable for applications using a ﬁxed power source (with a +/-10% variation) between 3 and 5V.

IN1+ IN1-

GS1 IN2+ IN2-

GS2

REF

FSKen+Tip/Ring CASen

PWDN

Bias Generator

Oscillator

OSC1 OSC2

Hybrid CASen

MODE

PWDN

Anti-Alias Filter

PWDN

FSKen

Control Bit Decode

CB1

CB0

PWDN

CASen

CB2

FSK Bandpass

FSKen CASen

2130Hz Bandpass

2750Hz Bandpass

CASen

Figure 1 - Functional Block Diagram

FSK Demodulator

Carrier Detector

Tone Detection Algorithm

MODE

Data Timing Recovery

STD

Guard Time

Mux

DATA DCLK

DR/STD

ST/GT

EST

Vdd Vss

MT88E45 Advance Information

REF

IN1+

IN1-

GS1

Vss OSC1 OSC2

CB0

DCLK DATA

1 2 3 4 5 6 7 8 9 10

MT88E45

20 19 18 17 16 15 14 13 12 11

Figure 2 - Pin Connections

Pin Description

Pin # Name Description

2 IN1+ Tip/Ring Op-amp Non-inverting (Input).

Voltage Reference (Output). Nominally Vdd/2. It is used to bias the Tip/Ring and Hybrid input

REF

op-amps.

IN2+ IN2GS2 CB2

CB1 Vdd

CD ST/GT

EST DR/STD

3 IN1- Tip/Ring Op-amp Inverting (Input). 4 GS1 Tip/Ring Gain Select (Output). This is the output of the Tip/Ring connection op-amp. The op-

amp should be used to connect the MT88E45 to Tip and Ring. The Tip/Ring signal can be ampliﬁed or attenuated at GS1 via selection of the feedback resistor between GS1 and IN1-. FSK demodulation (which is always on Tip/Ring) or CAS detection (f or MEI or BT on-hook CLIP) of the

GS1 signal is enabled via the CB1 and CB2 pins. See Tables 1 and 2. 5 Vss Power supply ground. 6 OSC1 Oscillator (Input). Crystal connection. This pin can also be driven directly from an external clock

source. 7 OSC2 Oscillator (Output). Crystal connection. When OSC1 is driven by an external clock, this pin

should be left open. 8 CB0 Control Bit 0 (CMOS Input). This pin is used primarily to select the 3-wire FSK data interface

mode. When it is low, interface mode 0 is selected where the FSK bit stream is output directly.

When it is high, interface mode 1 is selected where the FSK byte is stored in a 1 byte b uffer which

can be read serially by the application’s microcontroller.

The FSK interface is consisted of the DATA, DCLK and DR/STD pins. See the 3 pin descriptions

to understand how CB0 affects the FSK interface.

When CB0 is high and CB1, CB2 are both low the MT88E45 is put into a power down state

consuming minimal power supply current. See Tables 1 and 2. 9 DCLK 3-wire FSK Interface Data Clock (Schmitt Input/CMOS Output). In mode 0 (when the CB0 pin

is logic low) this is a CMOS output which denotes the nominal mid-point of a FSK data bit.

In mode 1 (when the CB0 pin is logic high) this is a Schmitt trigger input used to shift the FSK data

byte out to the DATA pin.

Advance Information MT88E45

Pin Description

Pin # Name Description

10 DATA 3-wire FSK Interface Data (CMOS Output). Mark frequency corresponds to logical 1. Space

frequency corresponds to logical 0. In mode 0 (when the CB0 pin is logic low) the FSK serial bit stream is output to the DATA pin directly. In mode 1 (when the CB0 pin is logic high) the start bit is stripped off, the data byte and the trailing stop bit are stored in a 9 bit buffer. At the end of each word signalled by the DR/STD pin, the microcontroller should shift the byte out onto the DATA pin by applying 8 read pulses to the DCLK pin. A 9th DCLK pulse will shift out the stop bit for framing error checking.

11 DR/STD 3-wire FSK Interface Data Ready/CAS Detection Delayed Steering (CMOS Output). Active

low. When FSK demodulation is enabled via the CB1 and CB2 pins this pin is the Data Ready output. It denotes the end of a word. In both FSK interface modes 0 and 1, it is normally hi and goes low for half a bit time at the end of a word. But in mode 1 if DCLK starts during DR low, the ﬁrst rising edge of the DCLK input will return DR to high. This feature allows an interrupt requested by a low going DR to be cleared upon reading the ﬁrst DATA bit. When CAS detection is enabled via the CB1 and CB2 pins this pin is the Delayed Steering output. It goes low to indicate that a time qualiﬁed CAS has been detected.

12 EST CAS Detection Early Steering (CMOS Output). Active high. This pin is the raw CAS detection

output. It goes high to indicate the presence of a signal meeting the CAS accept frequencies and signal level. It is used in conjunction with the ST/GT pin and external components to time qualify the detection to determine whether the signal is a real CAS.

13 ST/GT CAS Detection Steering/Guard Time (CMOS Output/Analog Input). It is used in conjunction

with the EST pin and external components to time qualify the detection to determine whether the signal is a real CAS. A voltage greater than V detected by asserting the DR/STD pin low. A voltage less than V accept a new CAS and returns DR/STD to high.

14 CD Carrier Detect (CMOS Output). Active low.

A logic low indicates that an FSK signal is present. A time hysteresis is provided to allow for momentary signal discontinuity. The demodulated FSK data is inhibited until carrier detect has

been activated. 15 Vdd Positive power supply. 16 CB1 Control Bit 1 (CMOS Input). Together with CB2 this pin selects the MT88E45’s functionality

between FSK demodulation, Tip/Ring CAS detection and Hybrid CAS detection.

When CB0 is high and CB1, CB2 are both low the MT88E45 is put into a power down state

consuming minimal power supply current. See Tables 1 and 2. 17 CB2 Control Bit 2 (CMOS Input). Together with CB1 this pin selects the MT88E45’s functionality

between FSK demodulation, Tip/Ring CAS detection and Hybrid CAS detection.

When CB0 is high and CB1, CB2 are both low the MT88E45 is put into a power down state

consuming minimal power supply current. See Tables 1 and 2. 18 GS2 Hybrid Gain Select (Output). This is the output of the hybrid receive connection op-amp. The op-

amp should be used to connect the MT88E45 to the telephone hybrid or speech IC receive pair.

The hybrid receive signal can be ampliﬁed or attenuated at GS2 via selection of the feedback

resistor between GS2 and IN2-. When the CPE is off-hook CAS detection of the GS2 signal

should be enabled via the CB1 and CB2 pins. See Tables 1 and 2.

at this pin causes the MT88E45 to indicate that a CAS has been

TGt

frees up the MT88E45 to

TGt

19 IN2- Hybrid Op-amp Inverting (Input). 20 IN2+ Hybrid Op-amp Non-Inverting (Input).

MT88E45 Advance Information

CB0 CB1 CB2

0/1 1 1 Set by CB0 FSK Demodulation. Tip/Ring input (GS1) selected. DR/STD is DR. 0/1 1 0 Set by CB0 Hybrid CAS Detection. Hybrid Receive input (GS2) selected. DR/STD is STD. 0/1 0 1 Set by CB0 Tip/Ring CAS Detection. Tip/Ring input (GS1) selected. DR/STD is STD.

1 0 0 Mode 1 Power Down. The MT88E45 is disabled and draws virtually no power supply

0 0 0 Mode 0 Reserved for factory testing.

The number of control bits (CB) required to interface the MT88E45 with the microcontroller depends on the functionality of the application, as shown in Table 2.

Functionality Group Controls Description

FSK (mode 0 or 1) and Hybrid CAS only (Non MEI compatible)

FSK

Interface

Function

When the line is off-hook, a Bellcore Multiple Extension Interworking (MEI) compatible Type 2 CPE should be able to detect CAS from Tip/Ring while the CPE is on-hook because it may be the ACK sender. Tip/Ring CAS detection is also required for BT’s on-hook CLIP.

current.

Table 1 - CB0/1/2 Functionality

CB2 CB0 is hardwired to Vdd or Vss to select the FSK

interface. CB1 hardwired to Vdd. The microcontroller uses CB2 to select between the 2 functions.

FSK (mode 0 or 1), Hybrid CAS, Tip/Ring CAS (MEI compatible or BT on-hook CLIP)

FSK (mode 1), Hybrid CAS, Tip/Ring CAS, Power Down (MEI compatible or BT on-hook CLIP)

FSK (mode 0), Hybrid CAS, Tip/Ring CAS, Power Down (MEI compatible or BT on-hook CLIP)

Table 2 - Control Bit Functionality Groups

CB1 CB2

CB0 CB1 CB2

Functional Overview

The MT88E45 is compatible with FSK and FSK plus CAS (CPE Alerting Signal) based Caller ID ser vices around the world. Caller ID is the generic name for a group of services offered by telephone operating companies whereby information about the calling party is delivered to the subscriber. In Europe and some other countries Caller ID is known as Calling Line Identity Presentation (CLIP). ETSI calls CAS ‘Dual Tone Alerting Signal’ (DT-AS), BT calls it ‘Tone Alert Signal’.

Depending on the service, data delivery can occur when the line is in the on-hook or off-hook state. In

CB0 is hardwired to Vdd or Vss to select the FSK interface. The microcontroller uses CB1 and CB2 to select between the 3 functions.

CB0 is hardwired to Vdd to select FSK interface mode 1. The microcontroller uses CB1 and CB2 to select between the 4 functions.

All 3 pins are required.

most countries the data is modulated in either Bell 202 or CCITT V.23 FSK format and transmitted at 1200 baud from the serving end ofﬁce to the subscriber’s terminal. Additionally in off-hook signalling, the special dual tone CAS is used to alert the terminal before FSK data transmission. BT uses CAS to alert the terminal prior to FSK in both onhook (Idle State) and off-hook (Loop State) signalling.

In North America, Caller ID uses the voiceband data transmission interface deﬁned in the Bellcore document GR-30-CORE. The terminal or CPE (Customer Premises Equipment) requirements are deﬁned in Bellcore document SR-TSV-002476. Typical services are CND (Calling Number Delivery),

Advance Information MT88E45

CNAM (Calling Name Delivery), VMWI (Visual Message Waiting Indicator) and CIDCW (Calling Identity Delivery on Call Waiting).

In Europe, Caller ID requirements are deﬁned by ETSI. The CPE documents are ETS 300 778-1 for on-hook, ETS 300 778-2 for off-hook. The end ofﬁce requirements are ETS 300 659-1 (on-hook) and ETS 300 659-2 (off-hook). ETSI has deﬁned services such as CLIP and CLIP with Call Waiting which are similar to those of Bellcore. Some European countries produce their own national speciﬁcations. For example, in the UK BT’s standards are SIN227 and SIN242, the UK CCA (Cable Communications Association) standard is TW/P&E/312.

In on-hook Caller ID, such as CND, CNAM and CLIP, the information is typically transmitted (in FSK) from the end ofﬁce before the subscriber picks up the phone. There are various methods such as between the ﬁrst and second rings (North Amer ica), between an abbreviated ring and the ﬁrst true ring (Japan, France and Germany). On-hook Caller ID can also occur without ringing for services such as VMWI. In BT’s on-hook CLIP, the signalling begins with a line polarity reversal, followed by CAS and then FSK. Bellcore calls an on-hook capable Caller ID CPE a ‘Type 1 CPE’.

In off-hook Caller ID, such as CIDCW and CLIP with Call Waiting, information about a new calling party is sent to the subscriber who is already engaged in a call. Bellcore’s method uses CAS to alert the CPE. When the CPE detects CAS and there are no offhook extensions, the CPE should mute its transmission path and send an acknowledgment to the end ofﬁce via a DTMF digit called ACK. Upon receiving ACK, the end ofﬁce will send the FSK data. Bellcore calls an off-hook capable CPE a ‘Type 2 CPE’. A Type 2 CPE is capable of off-hook and Type 1 functionalities and should ACK with a DTMF ‘D’. The ETSI and BT off-hook signalling protocols are similar to Bellcore’s but with timing and signal parametric differences. ETSI has no requirement for off-hook extension checking before ACK.

One factor affecting the quality of the CIDCW service is the CPE’s CAS speech immunity. Although the end ofﬁce has muted the far end party before and after it sends CAS, the near end (the end which is to receive the information) user may be still talking. Therefore the CPE must be able to detect CAS successfully in the presence of near end speech. This is called the talkdown immunity. The CPE must also be immune to imitation of CAS by speech from both ends of the connection because the CAS detector is continuously exposed to speech throughout the call. This is called the talkoff immunity.

If the CPE is a telephone, one way to achieve good CAS speech immunity is to put CAS detection on the telephone hybrid or speech IC receive pair instead of on Tip and Ring. Talkdown immunity improves because the near end speech has been attenuated while the CAS level is the same as on Tip/Ring, resulting in improved signal to speech ratio. Talkoff immunity is also improved because the near end speech has been attenuated.

In the present Bellcore off-hook protocol, the CPE should not ACK if it detected an off-hook extension. The FSK will not be sent and the customer will not receive a paid for service. Bellcore, in conjunction with the TIA (Telecommunications Industry Association) TR41.3.1 working group, has deﬁned a CPE capability called Multiple Extension Interworking (MEI) which will overcome this problem.

In the MEI scheme, all MEI compatible CPE’s must be capable of detecting CAS when the line is offhook, even though the CPE itself may be on-hook. This is because under some conditions an on-hook CPE may become the ACK sender. Another reason for the on-hook CPE to detect CAS is to maintain synchronous call logs between on and off-hook CPEs. When CAS is received and all off-hook CPEs are MEI compatible, one of the CPEs will ACK and all compatible sets will receive FSK.

A problem arises in a CPE where the CAS detector is connected only to the hybrid or speech IC receive pair: it cannot detect CAS when it is on-hook. The reason is that when the CPE is on-hook either the hybrid/speech IC is non functional or the signal level is severely attenuated. Therefore an on-hook Type 2 CPE must be capable of detecting CAS from Tip/ Ring, in addition to detecting CAS from the hybrid/ speech IC receive signal when it is off-hook.

The MT88E45 offers an optimal solution which combines good speech immunity and MEI compatibility. Two input op-amps allow the MT88E45 to be connected both to Tip/Ring and to the hybrid/ speech IC receive pair. Both connections can be differential or single ended. FSK demodulation is always on the Tip/Ring signal. CAS detection can be from the Tip/Ring or hybrid/speech IC receive signal. Being able to detect CAS on Tip/Ring also makes the MT88E45 suitable for BT on-hook CLIP applications.

For applications such as those in most European countries where Tip/Ring CAS detection is not needed, then the Tip/Ring and Hybrid op-amp gains can be tailored independently to meet country speciﬁc FSK and CAS signal level requirements respectively. Note that since the Hybr id op-amp is for

MT88E45 Advance Information

CAS detection only, its gain can always be tailored speciﬁcally for the CAS signal level.

The FSK demodulator is compatible with Bellcore, ETSI and BT standards. The demodulated FSK data is either output directly (bit stream mode) or stored in a one byte buffer (buffer mode). In the buffer mode, the stop bit immediately following a byte is also stored and can be shifted out after the data byte. This facility allows for framing error checking required in Type 2 CPEs. In the bit stream mode, two timing signals are provided. One indicates the bit sampling instants of the data byte, the other the end of byte. A carrier detector indicates presence of signal and shuts off the data stream when there is no signal.

The entire chip can be put into a virtually zero current power down mode. The input op-amps, FSK demodulator, CAS detector and the oscillator are all shut off. Furthermore, power management has been incorporated to minimize operating current. When FSK is selected the CAS detector is powered down. When CAS is selected the FSK demodulator is powered down.

Functional Description

hook CLIP, while Hybrid CAS detection is needed for optimal CAS speech immunity.

The feedback resistor connected between GS1 and IN1- can be used to adjust the Tip/Ring signal gain. The feedback resistor connected between GS2 and IN2- can be used to adjust the hybrid receive signal gain. When the Tip/Ring op-amp is selected, the GS2 signal is ignored. When the Hybrid op-amp is selected, the GS1 signal is ignored.

Either or both op-amps can be conﬁgured in the single ended input conﬁguration shown in Figure 3, or in the differential input conﬁguration shown in Figure 4.

IN+

Voltage Gain

(AV) = RF / R

Highpass Corner Frequency

= 1/(2πRINC)

-3dB

IN-

REF

Figure 3 - Single Ended Input Conﬁguration

3 to 5V Operation

The MT88E45’s FSK and CAS reject levels are proportional to Vdd. When operated at Vdd equal 3V +/- 10%, to keep the FSK and CAS reject levels as at 5V (nominal) the Tip/Ring and Hybrid op-amp gains should be reduced from those of 5V. Gains for nominal Vdd (with a +/- 10% variation) other than 3 or 5V can be chosen as interpolation between the 3 and 5V settings.

Input Conﬁguration

The MT88E45 provides an input arrangement comprised of two op-amps and a bias source (V V

is a low impedance voltage source which is

REF

used to bias the op-amp inputs at Vdd/2. The Tip/ Ring op-amp (IN1+, IN1-, GS1 pins) is for connecting to Tip and Ring. The Hybrid op-amp (IN2+, IN2-, GS2 pins) is for connecting to the telephone hybrid or speech IC receive pair.

Either FSK or CAS detection can be selected for the Tip/Ring connection, while the hybrid connection is for CAS detection only. Phrased in another way, FSK demodulation is always on Tip/Ring, while CAS detection can be on Tip/Ring or Hybrid Receive. Tip/ Ring CAS detection is required for MEI and BT on-

Differential Input Ampliﬁer

C1 = C2 R1 = R4 (For unity gain R5= R4) R3 = (R2R5) / (R2 + R5)

Voltage Gain

diff) = R5/R1

Input Impedance

diff) = 2

+ (1/ωC)

Highpass Corner Frequency

= 1/(2πR1C1)

-3dB

IN+

IN-

REF

Figure 4 - Differential Input Conﬁguration

CAS Detection

In North America, CAS is used in off-hook signalling only. In Europe (ETSI) it is used in off-hook signalling, and by BT in both on and off-hook signalling. ETSI calls it the Dual Tone Alerting Signal (DT-AS). Although the ETSI on-hook standard contains a DT-AS speciﬁcation, BT is the only administration known to employ CAS in on-hook

Advance Information MT88E45

2130 Hz and 2750 Hz

CAS/DT-AS Characteristics

Bellcore

(Off-hook only)

(Off-hook)

ETSI

(Off-hook = ‘Loop State’)

(On-hook = ‘Idle State’)

Frequency Tolerance +/-0.5% +/-0.5% Off-hook: +/-0.6%

On-hook: +/-1.1%

Signal Level (per tone) -14 to -32 dBm

-9.78 to -32.78 dBm

+0.22 to -37.78 dBm

(-12 to -35 dBVe)

Reject Level (per tone) -45 dBm On-hook: -43.78 dBm

(-2 to -40 dBV)

(-46 dBV)

Maximum Twist (V

2130Hz/V2750Hz

) +/-6 dB +/-6 dB +/-7 dB

Duration 75 to 85 ms 75 to 85 ms Off-hook: 80 to 85 ms

On-hook: 88 to 110 ms

Reject Duration Off-hook: <=70 ms

On-hook: <=20 ms

Signal to Noise Ratio Speech Speech Off-hook: Speech

On-hook: >= 20 dB

(300-3400 Hz)

Hybrid Op-amp (GS2) Gain

0 dB 0 dB 0 dB

Vdd = 5V +/- 10% Hybrid Op-amp (GS2) Gain

-3.5 dB -3.5dB TBD

Vdd = 3V +/- 10%

a. SR-TSV-002476, Issue 1 Dec 1992 b. ETS 300 778-2 Jan 98. The DT-AS plus FSK variant of ETSI on-hook signalling described in ETS 300 778-1 is not supported

because on-hook DT-AS uses the GS1 op-amp. With the GS1 gain in Table 4, the minimum DT-AS level will be below the

MT88E45’s minimum accept level. c. SIN227 Issue 3 Nov 97, SIN242 Issue 2 Nov 96 d. dBm - Decibels above or below a reference power of 1 mW into 600 ohms. 0 dBm = 0.7746 Vrms. e. dBV - Decibels above or below a reference voltage of 1 Vrms. 0 dBV = 1 Vrms

Table 3 - CAS/DT-AS Characteristics

signalling. (BT calls it Tone Alert Signal.) The CAS/ DT-AS characteristics are summarized in Table 3.

is key to good speech immunity. The ﬁrst indication that there might be a CAS is when EST goes high. EST high indicates that both tones are present. EST

Table 3 shows the Hybrid op-amp gain for operation at 3V and 5V nominal Vdd, with a ± 10% Vdd variation. For 3V operation, the Hybrid op-amp gain should be reduced from the 5V setting to maintain

low indicates that one or both tones is not present. STD low indicates that CAS has been detected. When STD returns high it indicates that CAS has ended.

the CAS reject level and to maintain the talkoff immunity: the CAS threshold is directly proportional to Vdd, when Vdd is reduced the threshold becomes lower, hence lower level CAS are accepted. If the gain is not reduced, the MT88E45 will be more talkoff prone.

The timing algorithm consists of 2 components: a tone present guard time (tGP) and a tone absent guard time (tGA). tGP sets the minimum accept duration for CAS. That is, both tones must be detected continuously for tGP for STD to go low to indicate that CAS has been detected. For STD to

When CAS detection is selected, the dual purpose output pin DR/STD is STD. STD goes low when CAS has been detected, and returns high after CAS has ended.

return high to indicate that CAS has ended, one or both tones must have disappeared for tGA. The purpose of tGA is to bridge over momentary EST dropouts once EST has met the minimum tone duration so as to decrease the likelihood of a long talkoff being broken up into several talkoffs. Usually

CAS Guard Time

tGA is set very short or removed altogether because

there is another way to deal with the problem (by The guard time circuit shown in Figure 5 implements a timing algorithm which determines whether the

ignoring further detections for 2 seconds after every

detection). signal is a CAS. Proper selection of the guard time(s)

MT88E45 Advance Information

Both Tones Present

CAS

EST

ST/GT

MT88E45

Comparator

REC

VTGt

= Vss

ABS

=R1C ln [Vdd / (Vdd-VTGt)]

=RpC ln Vdd - Vdiode (Rp/R2)

Rp=R1 || R2

=0 if R2=0

Vdd

ST/GT

diode

EST

Rp=R1 || R2

DR/STD Indicates STD in CAS

detection mode

VTGt - Vdiode (Rp/R2)

STD

Figure 5 - CAS Guard Time Circuit Operation

Tone present guard time (tGP) operation: In Figure 5 initially there is no CAS, EST is low so Q1 is off. C has been fully charged applying 0V to ST/GT so Q2 is on. When both tones are detected EST goes high and turns off Q2. Because C has been fully charged (ST/GT=0V), the comparator output is low and Q1 stays off. With both Q1 and Q2 off the high at EST discharges C through R1 and the ST/GT voltage increases from 0V. When the voltage exceeds the comparator threshold VTGt, which is typically 0.5 Vdd, the comparator output goes high; Q1 turns on and accelerates the discharge of C (ST/GT goes quickly to Vdd); STD goes low to indicate that a valid CAS has been received. If one or both tones disappeared before tGP has been reached (i.e. when ST/GT voltage is still below VTGt), Q2 turns back on and charges C quickly to bring the ST/GT voltage back to 0V. Then if EST goes high again the t

duration must start over.

Tone absent guard time (tGA) operation: In Figure 5 initially both tones have been detected for tGPso C is fully discharged and ST/GT is at Vdd. While both tones continue to be detected EST stays high; ST/

GT is at Vdd (the comparator output is high); so Q1 is on and Q2 is off. When one or both tones stop EST goes low and turns off Q1. Because C is fully discharged (ST/GT=Vdd), the comparator output is high and Q2 stays off. With both Q1 and Q2 off the low at EST charges C through Rp=(R1 || R2) and the ST/GT voltage falls towards 0V. When the voltage has fallen below VTGt, the comparator output goes low. Since EST is also low Q2 turns on and accelerates the charging of C so that ST/GT goes quickly to 0V. STD goes high to indicate that the CAS has ended. If EST goes back to high before tGA has been reached (i.e. when ST/GT voltage is still above V

), Q1 turns back on and discharges C quickly to

TGt

bring the ST/GT voltage back to Vdd. Then if EST goes low again the tGA duration must start over. To set tGA=0, set R2 to 0.

In Figure 5, tDP is the delay from the start of CAS to EST responding, tDA is the delay from the end of CAS to EST responding. The total delay from the start of CAS to STD responding is t

REC=tDP+tGP.

The total delay from the end of CAS to STD responding is t

ABS=tDA+tGA

Advance Information MT88E45

Parameter North America: Bellcore

Europe: ETSI

UK: BT

Mark (Logical 1) Frequency 1200 Hz +/- 1% 1300 Hz +/- 1.5% Space (Logical 0) Frequency 2200 Hz +/- 1% 2100 Hz +/- 1.5% Received Signal Level -4.23 to -36.20 dBm

(476 to 12 mVrms)

Signal Reject Level -48.24 dBm (3mVrms) for

On-hook No Ring Signalling

-5.78 to -33.78 dBm (-8 to -36 dBV)

On-hook: -47.78 dBm

(-50dBV)

f,g

-5.78 to -37.78 dBm (-8 to -40 dBV)

such as VMWI Transmission Rate 1200 baud +/- 1% 1200 baud +/- 1% Twist (V

MARK/VSPACE

Signal to Noise Ratio Single Tone (f):

) -6 to +10 dB -6 to +6 dB

>= 25 dB

-18 dB (f<=60Hz)

(300 to 3400 Hz)

>= 20 dB

(300 to 3400 Hz)

-12 dB (60<f<=120Hz)

-6 dB (120<f<=200Hz)

+25 dB (200<f<3200Hz)

+6 dB (f>=3200Hz)

Tip/Ring Op-Amp (GS1) Gain

0 dB -2 dB

0 dB

Vdd = 5V +/- 10% Tip/Ring Op-Amp (GS1) Gain

-3.5 dB -5.5 dB

TBD

Vdd = 3V +/- 10%

a. ANSI/TIA/EIA-716 and draft TIA/EIA-777. Bellcore has agreed to the values and will synchronize its requirements. b. ETS 300 778-1 (On-hook) Sep 97, ETS 300 778-2 (Off-hook) Jan 98. c. SIN 227 Issue 3 Nov 97, SIN242 Issue 2 Nov 96. d. Nor th Amer ican on-hook signalling range. The off-hook range is inside the on-hook range: 190mVrms to 12mVrms. e. dBm - Decibels above or below a reference power of 1 mW into 600 ohms. 0 dBm = 0.7746 Vrms f. dBV - Decibels above or below a reference voltage of 1 Vrms. 0 dBV = 1 Vrms. g. ETSI on-hook signalling range. The off-Hook signalling levels are inside this range: -8.78 to -30.78 dBm (-11 to -33 dBV). h. The 5V ETSI Tip/Ring op-amp gain can be 0 dB if there is no FSK reject level requirement. i. The 3V ETSI Tip/Ring op-amp gain can be -3.5dB if there is no FSK reject level requirement.

Table 4 - FSK Signal Characteristics

FSK Demodulation

The FSK characteristics are shown in Table 4. In North America, TIA (Telecommunications Industry Association) also deﬁnes standards. The Type 1 Caller ID CPE standard is ANSI/TIA/EIA-716. The Type 2 standard is being drafted to become TIA/EIA-

777. The North American FSK characteristics in Table 4 are from ANSI/TIA/EIA-716. They differ from those Bellcore published in SR-TSV-002476 and SR-

3004. Bellcore is represented in TR41.3.1 and will synchronize to the TIA requirements in its future documents.

The TIA Type 1 standard includes an FSK reject level:

• if data is not preceded by ringing (e.g. VMWI), FSK signals below 3mVrms (-48.24 dBm) shall be rejected

• if data is preceded by ringing, FSK detection may be extended below 3mVrms

The MT88E45 is compliant with the Bellcore/TIA, ETSI and BT requirements with the Tip/Ring op-amp gains in Table 4. In Europe if the country speciﬁc FSK requirements do not incorporate ETSI’s FSK reject level then the Tip/Ring op-amp gain can also be 0dB at 5V and -3.5dB at 3V to meet the ETSI minimum CAS level for on-hook signalling (-40 dBV).

For 3V operation, the FSK receiver becomes more sensitive and lower level signals will be accepted than at 5V. To maintain the FSK reject level, the Tip/ Ring input op-amp gain should be reduced. Note that since the Tip/Ring op-amp is also used for Tip/Ring CAS detection, the CAS level will also be reduced for on-hook detection.

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