MT88L85AN1 데이터 시트보기 (PDF) - Microsemi Corporation

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MT88L85AN1

3 V Integrated DTMF Transceiver with Power-Down and Adaptive Micro Interface

Microsemi Corporation 

MT88L85

Data Sheet

For applications which are required to meet a guaranteed RX input level of -29 dBm over the full temperature and

supply voltage range, a unity gain input configuration as shown in Figures 3 and 4 can be used.

For applications which require signal detection lower than -29 dBm, the external resistors can be configured to give

adequate gain. For example, if the application requires tone detection of -31dB, the input gain can be set to

+2 dB with the external resistors (see Figures 13 and 14 for value of resistors). However, when +2 dB gain is used,

the corresponding maximum input signal level must not exceed -6 dBm.

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). The filters also 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.

MT88L85

IN+

C

RIN

IN-

VOLTAGE GAIN

(AV) = RF / RIN

RF

GS

VRef

Figure 3 - Single-Ended Input Configuration

C1

R1

MT88L85

IN+

C2

R4

IN-

R5

GS

R3

R2

VRef

DIFFERENTIAL INPUT AMPLIFIER

C1 = C2

R1 = R4

R3 = (R2R5)/(R2 + R5)

VOLTAGE GAIN

(AV diff) = R5/R1

FOR UNITY

R5=R1

INPUT IMPEDANCE

(ZINdiff) = 2 R12 + (1/ωC)2

Figure 4 - Differential Input Configuration

4

Zarlink Semiconductor Inc.

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