Philips Semiconductors
Product specification
Analog voice scrambler/descrambler
CONTENTS
1
2
3
6
6.1
6.2
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
8
8.1
8.2
8.3
8.4
8.5
9
10
11
12
14.1
14.2
14.3
14.4
15
16
17
FEATURES
APPLICATIONS
GENERAL DESCRIPTION
PINNING INFORMATION
Pinning
Pin description
Scrambling
Power supply (V
DD
, V
SS
)
Oscillator (OSCI)
Splitting frequency and mode selection
Serial clock input (SCL), Serial data input (SDA)
Address input (A0)
I
2
C-bus data configuration
Signal input (IN), Signal output (OUT)
I
2
C BUS INTERFACE
Bit transfer
Start and stop conditions
System configuration
Acknowledge
Timing specifications
APPLICATIONS
HANDLING
LIMITING VALUES
CHARACTERISTICS
Introduction
Reflow soldering
Wave soldering
Repairing soldered joints
DEFINITIONS+
LIFE SUPPORT APPLICATIONS
PURCHASE OF PHILIPS I
2
C COMPONENTS
PCD4440T
1996 Dec 20
2
Philips Semiconductors
Product specification
Analog voice scrambler/descrambler
1
FEATURES
2
APPLICATIONS
PCD4440T
•
Scrambler or descrambler function
•
Scrambling in frequency domain
•
Selectable split frequency (up to 10 selections per
second)
•
Telephony-band filtering included
•
No increase in bandwidth
•
No external components required
•
Small signal delay
•
Insensitive to distortion and group delay of transmission
channel
•
Control via serial I
2
C-bus
•
Low transfer loss of speech
•
Mute option
•
Transparent mode
•
High signal input impedance
•
Low signal output impedance
•
Low power consumption.
4
ORDERING INFORMATION
TYPE
NUMBER
PCD4440T
•
Cordless telephones
•
Security telephones
•
Portable phones
•
Private Mobile Radio (PMR).
3
GENERAL DESCRIPTION
The PCD4440T is a silicon gate CMOS integrated circuit
intended to be used in cordless telephony, radio, and line
telecommunications products utilizing a microcontroller for
the control functions. The purpose of the device is to
prevent unauthorized ‘listening-in’ on conversations.
A major application is protection of the vulnerable radio link
between a CT0 type cordless handset and its base unit.
Analog scrambling/descrambling is based on the split
frequency method realized in a sophisticated
switched-capacitor technology. The PCD4440T is
compatible with most microcontrollers and communicates
via a two line bidirectional I
2
C-bus.
PACKAGE
NAME
SO8
DESCRIPTION
plastic small outline package; 8 leads; body width 7.5 mm
VERSION
SOT176-1
1996 Dec 20
3
Philips Semiconductors
Product specification
Analog voice scrambler/descrambler
6
6.1
PINNING INFORMATION
Pinning
7.1
Scrambling
PCD4440T
handbook, halfpage
SCL 1
SDA 2
8 A0
7
OSCI
VDD
OUT
PCD4440T
VSS
IN
3
4
MGG728
6
5
The PCD4440Taccomplishes this task by first filtering the
incoming signal, limiting the bandwidth to 3500 Hz. Then
the signal is split into a high (> f
s
) and a low (< f
s
) frequency
band. Both frequency bands are inverted and added again
to provide a single output signal. Values for 9 split
frequencies f
S
can be controlled by a scramble code table
in the microcontroller. Control of these split frequencies is
accomplished via the serial two-wire I
2
C-bus. In addition to
the split frequencies (f
s
), a transparent mode and mute
instruction can be selected (see Table 1).
Figure 3 shows the signal path for both bands. The lower
band path (on the left side of the diagram) operates on
frequencies f
≤
f
s
(Split Frequency), the upper band path
(on the right side) on frequencies f
≥
f
s
.
The input signal contains frequencies from f
1
up to f
2
.
In scrambling mode, the output signal is band limited from
f
l
(300 Hz) to f
h
(3500 Hz). In the left path, the input signal
is first limited to f
s
. The following modulator inverts the
lower band. f
l
is folded up to f
s
, f
s
down to f
l
. In general, an
input frequency f
in
is folded to f
out
= f
s
+ f
l
−
f
in
. Finally the
folded signal is band limited to f
s
again.
In the right path, the input signal is first limited to f
h
.
The following modulator inverts the upper band. f
s
is folded
up to f
h
, f
h
down to f
s
. In general, an input frequency f
in
is
folded to f
out
= f
s
+ f
h
−
f
in
. Finally, the folded signal is band
limited to f
h
again. In the last step, the bands are added
and buffered.
Because of the symmetry of the scrambling process,
descrambling is achieved by passing the signal through
another PCD4440T.
In the transparent mode, the input signal is band limited to
3500 Hz. Frequencies from 0 to 300 Hz are not filtered
out.
Fig.2 Pin configuration.
6.2
Pin description
PIN
1
2
3
4
5
6
7
8
TYPE
I
I
P
I
O
P
I
I
DESCRIPTION
serial clock line (I
2
C-bus)
serial data line (I
2
C-bus)
negative Supply
signal input
signal output
positive supply
oscillator input
slave address input (I
2
C-bus)
SYMBOL
SCL
SDA
V
SS
IN
OUT
V
DD
OSCI
A0
7
FUNCTIONAL DESCRIPTION
To provide privacy for the end user of a cordless telephone
set, the radio-link audio signal must be scrambled. In the
microphone of the handset and the incoming telephone
line audio path of the base unit a scrambler circuit has to
be implemented. Consequently the audio signal to the
telephone line and to the earpiece must be descrambled.
Both functions can be fulfilled by the PCD4440T by simply
inserting it in the audio path.
1996 Dec 20
5
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