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MT8889CN Datasheet(PDF) 3 Page - Mitel Networks Corporation |
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MT8889CN Datasheet(HTML) 3 Page - Mitel Networks Corporation |
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3 / 18 page  MT8889C/MT8889C-1 4-109 Functional Description The MT8889C/MT8889C-1 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 adaptive micro interface allows microcontrollers, such as the 68HC11, 80C51 and TMS370C50, to access the MT8889C/MT8889C-1 internal registers. Input Configuration The input arrangement of the MT8889C/MT8889C-1 provides a differential-input operational amplifier as well as a bias source (VRef), which is used to bias the inputs at VDD/2. Provision is made for connection of a feedback resistor to the op-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. 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. Figure 3 - Single-Ended Input Configuration C RIN RF IN+ IN- GS VRef VOLTAGE GAIN (AV) = RF / RIN MT8889C/ MT8889C-1 Figure 4 - Differential Input Configuration 0= LOGIC LOW, 1= LOGIC HIGH Table 1. Functional Encode/Decode Table FLOW FHIGH DIGIT D3 D2 D1 D0 697 1209 1 0 0 0 1 697 1336 2 0 0 1 0 697 1477 3 0 0 1 1 770 1209 4 0 1 0 0 770 1336 5 0 1 0 1 770 1477 6 0 1 1 0 852 1209 7 0 1 1 1 852 1336 8 1 0 0 0 852 1477 9 1 0 0 1 941 1336 0 1 0 1 0 941 1209 * 1 0 1 1 941 1477 # 1 1 0 0 697 1633 A 1 1 0 1 770 1633 B 1 1 1 0 852 1633 C 1 1 1 1 941 1633 D 0 0 0 0 C1 C2 R1 R2 R3 R4 R5 IN+ IN- GS VRef MT8889C/ DIFFERENTIAL INPUT AMPLIFIER C1 = C2 = 10 nF R1 = R4 = R5 = 100 k Ω R2 = 60k Ω, R3 = 37.5 kΩ R3 = (R2R5)/(R2 + R5) VOLTAGE GAIN (AV diff) - R5/R1 INPUT IMPEDANCE (ZINdiff) = 2 R1 2 + (1/ ωC)2 MT8889C-1 |
Similar Part No. - MT8889CN |
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Similar Description - MT8889CN |
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