mt88l89asr1 Zarlink Semiconductor, mt88l89asr1 Datasheet - Page 4

• Manufacturer Part Number: mt88l89asr1
• Description: 3 V Integrated Dtmf Transceiver With Adaptive Micro Interface
• Manufacturer: Zarlink Semiconductor

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.
DIFFERENTIAL INPUT AMPLIFIER
C1 = C2
R1 = R4
R3 = (R2R5)/(R2 + R5)
FOR UNITY GAIN
R5=R1
VOLTAGE GAIN
(A
V
) = R
Figure 3 - Single-Ended Input Configuration
Figure 4 - Differential Input Configuration
C2
C1
F
C
/ R
IN
R4
R1
R3
R
Zarlink Semiconductor Inc.
IN
MT88L89
VOLTAGE GAIN
INPUT IMPEDANCE
(Z
(A
R2
R5
IN
V
4
diff) = 2 R1
diff) = R5/R1
R
F
IN+
IN-
GS
V
Ref
MT88L89
IN+
IN-
GS
V
2
Ref
MT88L89
+ (1/ωC)
2
Data Sheet