MT3170B/71B, MT3270B/71B, MT3370B/71B

Data Sheet

3

Zarlink Semiconductor Inc.

Functional Description

The MT3x7xBs are high performance and low power consumption DTMF receivers. These devices provide wide

dynamic range DTMF detection and a serial decoded data output. These devices also incorporate an energy

detection circuit. An input voiceband signal is applied to the devices via a series decoupling capacitor. Following the

unity gain buffering, the signal enters the AGC circuit followed by an anti-aliasing filter. The bandlimited output is

routed to a dial tone filter stage and to the input of the energy detection circuit. A bandsplit filter is then used to

separate the input DTMF signal into high and low group tones. The high group and low group tones are then

verified and decoded by the internal frequency counting and DTMF detection circuitry. Following the detection

stage, the valid DTMF digit is translated to a 4-bit binary code (via an internal look-up ROM). Data bits can then be

shifted out serially by applying external clock pulses.

Automatic Gain Control (AGC) Circuit

As the device operates on a single power supply, the input signal is biased internally at approximately VDD/2. With

large input signal amplitude (between 0 and approximately -30 dBm for each tone of the composite signal), the

15

7

7

ESt

(MT3x70B)

DStD

(MT3x71B)

Early Steering Output. A logic high on ESt indicates that a DTMF

signal is present. ESt is at logic low in powerdown state.

Delayed Steering Output. A logic high on DStD indicates that a

valid DTMF digit has been detected. DStD is at logic low in

powerdown state.

18

8

8

Positive Power Supply (5 V Typ.) Performance of the device can

be optimized by minimizing noise on the supply rails. Decoupling

1,5,7,8,

10, 12,

14,16,

17

--

NC

No Connection. Pin is unconnected internally.

3-

2

PWDN Power Down Input. A logic high on this pin will power down the

device to reduce power consumption. This pin is pulled down

internally and can be left open if not used. ACK pin should be at logic

’0’ to power down device.

Summary of MT3x70/71B Product Family

Device

Type

8 Pin

18 Pin

20 Pin

PWDN

2 Pin

OSC

Ext

CLK

ESt

DStD

MT3170B

√√

√

√

MT3171B

√√

√

√

MT3270B

√

√√√

MT3271B

√√

√

√

MT3370B

√√√√√√

MT3371B

√√√√√

√

Pin Description

Pin #

Name

Description

337xB

327xB

317xB