Calling Line Identifier
FX602
1.5
1.5.1
General Description
Mode Control Logic
The FX602's operating mode and the source of the DET and IRQN outputs are determined by the logic levels
applied to the MODE and ZP input pins;
ZP
0
MODE
0
Mode
Tone Alert Detect
DET o/p from
Tone Alert Signal
Detection
FSK Level Detector
IRQN o/p from
End of Tone Alert Signal.
Ring or Line Polarity
Reversal Detector.
FSK Data Retiming [1].
Ring or Line Polarity
Reversal Detector.
Ring or Line Polarity
Reversal Detector.
-
0
1
FSK Receive
1
1
0
1
'Zero-Power'
'Zero-Power'
Ring or Line Polarity
Reversal Detector.
Ring or Line Polarity
Reversal Detector.
[1] If enabled.
In the 'Zero-Power' modes, power is removed from all of the internal circuitry except for the Ring or Line
Polarity Reversal Detector and the DET and IRQN outputs.
1.5.2
Input Signal Amplifier
This amplifier is used to convert the balanced FSK and Tone Alert signals received over the telephone line to
an unbalanced signal of the correct amplitude for the FSK receiver and Tone Alert Detector circuits.
Figure 3a : Input Signal Amplifier, balanced input configuration
The design equations for this circuit are;
Differential voltage gain VAOP / V(b-a) = R8/R6
R6 = R7 = 470k
Ω
R10 = 160k
Ω
R9 = R8 x R10 / (R8 - R10)
The target differential voltage gain depends on the expected signal levels between the A and B wires and the
FX602's internal threshold levels, which are proportional to the supply voltage.
The FX602 has been designed to meet the applicable specifications with R8 = 470k
Ω
at V
DD
= 3.3V nominal,
rising to 680k
Ω
at V
DD
= 5.0V, and R9 should be 240k
Ω
at V
DD
= 3.3V and 200k
Ω
at V
DD
= 5.0V as shown in
section 1.4 and Fig 3c.
©
1998 Consumer Microcircuits Limited
7
D/602/7
CMLMICRO [ CML MICROCIRCUITS ]
