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In DPSK mode the 73K322L modulates a serial bit stream into di-bit pairs that are represented by four possible phase shifts as prescribed by the V.22 standards. The base-band signal is then filtered to reduce intersymbol interference on the bandlimited 2-wire telephone line. Transmission occurs using either a 1200 Hz (Originate mode) or 2400 Hz carrier (Answer mode). Demodulation is the reverse of the modulation process, with the incoming analog signal eventually decoded into di-bits and converted back to a serial bit stream. The demodulator also recovers the clock which was encoded into the analog signal during modulation. Demodulation occurs using either a 1200 Hz carrier (Answer mode or ALB Originate mode) or a 2400 Hz carrier (Originate mode or ALB Answer mode). The 73K322L uses a phase locked loop coherent demodulation technique for optimum receiver performance.
Detector Circuits When DC bias is available, Schottky diode detector circuits can be used to create low cost RF and microwave receivers with a sensitivity of -55 dBm to -57 dBm.[1] Moreover, since external DC bias sets the video impedance of such circuits, they display classic square law response over a wide range of input power levels[2,3]. These circuits can take a variety of forms, but in the most simple case they appear as shown in Figure 12. This is the basic detector circuit used with the HSMS-286X family of diodes.
TDUHC124 is a precision isolation amplifier incorporating an uncommitted operational amplifier for input condi- tioning, a novel duty cycle modulation-demodulation technique and excellent accuracy. Internal input pro- tection can withstand up to 30V differential without damage. The signal is transmitted digitally across a differential capacitive barrier. With digital modulation the barrier characteristics do not affect signal integrity. This results in excellent reliability and good high frequency transient immunity across the barrier. Both the amplifier and barrier capacitors are housed in a plastic DIP.