FX118 Datasheet, PDF (4/7 Pages) CML Microcircuits – Duplex Frequency Inverter for Cordless Telephones

Application Information ......
+5 ^Gain
dB
0
-3
-10
-20
Audio Input Level = 275mVrms
V_DD = 3.75V
-30
-40
0.1
0.2
0.3
0.5
1.0
2.0
3.0
7.0
Frequency kHz
Fig.4 Typical Audio Frequency Response of a Single Scrambled or De-scrambled Channel
System Gains
When calculating the external components for the operation of the FX118 the following points should be considered:
(a) The Input Lowpass Filter has a (typical) gain of 0.5dB.
(b) The Balanced Modulator has a (typical) attenuation of 4.0dB.
(c) The Output Bandpass Filter has a (typical) gain of 4.5dB.
How the Inverter Works
Carrier Frequency minus Input Voice Frequency equals Scrambled Voice Frequency
(1)
(2)
B
A
C
Input Voiceband Frequencies
Lowpass Filtered Voiceband
D
for Input to
Balanced Modulator
Speech Band
0
1000Hz
2000Hz
3000Hz
(3)
(4)
B
Carrier Frequency (3300Hz)
Generated On-Chip for Input to
Balanced Modulator
C
A
D
Bandpass Filtered Voiceband
Presented at the Ouput
after Mixing with the Carrier Frequency
in the Balanced Modulator
0
1000
2000
3000 3300
0
1000
2000
3000
Fig.5 A Pictorial Explanation of the FX118 “Scramble Operation”
4