MT8888C

Data Sheet

3

Zarlink Semiconductor Inc.

1.0

Functional Description

The MT8888C Integrated DTMF Transceiver consists of a high performance DTMF receiver with an internal gain

setting amplifier and a DTMF generator which employs a burst counter to synthesize precise tone bursts and

pauses. A call progress mode can be selected so that frequencies within the specified passband can be detected.

The Intel micro interface allows microcontrollers, such as the 8080, 80C31/51 and 8085, to access the MT8888C

internal registers.

2.0

Input Configuration

The input arrangement of the MT8888C provides a differential-input operational amplifier as well as a bias source

amp output (GS) for gain adjustment. In a single-ended configuration, the input pins are connected as shown in

Figure 3. Figure 4 shows the necessary connections for a differential input configuration.

3.0

Receiver Section

Separation of the low and high group tones is achieved by applying the DTMF signal to the inputs of two sixth-order

switched capacitor bandpass filters, the bandwidths of which correspond to the low and high group frequencies

(see Table 1). These filters incorporate notches at 350 Hz and 440 Hz for exceptional dial tone rejection. Each filter

output is followed by a single order switched capacitor filter section, which smooths the signals prior to limiting.

Limiting is performed by high-gain comparators which are provided with hysteresis to prevent detection of

unwanted low-level signals. The outputs of the comparators provide full rail logic swings at the frequencies of the

incoming DTMF signals.

18

22

26

ESt

Early Steering output. Presents a logic high once the digital algorithm has

detected a valid tone pair (signal condition). Any momentary loss of signal

condition will cause ESt to return to a logic low.

19

23

27

St/GT

detected at St causes the device to register the detected tone pair and update the

The GT output acts to reset the external steering time-constant; its state is a

function of ESt and the voltage on St.

20

24

28

Positive power supply (5 V typical).

8, 9,

16,17

3,5,10,

11,16,

23,25

NC

No Connection.

Pin Description (continued)

Pin #

Name

Description

20

24

28