CML Semiconductor Products
PRODUCT INFORMATION
FX118
Features/Applications
Frequency Inversion Scrambling
Full-Duplex Operation
High Baseband and Carrier
Rejection
Audio Lowpass and Bandpass
Filtering On-Chip
Xtal Oscillator Stabilty
Duplex Frequency Inverter
for Cordless Telephones
Publication D/118/3 July 1994
Low Power Requirement
(3.0 Volt Minimum)
Cordless Telephones
Base and Handheld Applications
Input Gain Adjustment
Plastic DIL and S.O.I.C. Package
Styles
C1 AMP OUT
LPF(1)
LPF(1) OUT
B MOD(1) IN
BAL MOD (1)
BPF(1)
C1 IN
C1 OUT
+0.5dB
INPUT AMP
CHANNEL 1 (C1)
-4.0dB
+4.0dB
V
BIAS
XTAL/CLOCK
XTAL
CLOCKS
and
LOGIC
FILTER CLOCKS
111kHz
CARRIER
3.3kHz
V
DD
V
BIAS
V
SS
FX118
V
BIAS
INPUT AMP
CHANNEL 2 (C2)
-4.0dB
C2 OUT
C2 IN
+0.5dB
LPF(2)
BAL MOD (2)
+4.0dB
BPF(2)
C2 AMP OUT
LPF(2) OUT
B MOD(2) IN
Fig.1 FX118 Duplex Frequency Inverter
Brief Description
The FX118 is a low-power, full-duplex frequency
inverter available to provide voice privacy for cordless
telephone systems by mixing the incoming audio with an
internally produced carrier frequency (3.3kHz).
This chip contains two completely separate audio
channels (C1 and C2) each comprising a “component-
adjustable” input amplifier, a 10th-order lowpass filter, a
balanced modulator and a 14th-order bandpass filter
output.
The on-chip modulation process has the properties of
high baseband and carrier frequency rejection which
when combined with high-order output filtering,
produces a high-quality recovered voiceband audio.
1
The frequency stability of the FX118 is achieved by an
on-chip oscillator employing an external 4.433619MHz
Xtal or clock input to produce the common carrier
frequency and the sampling clocks for the switched
capacitor low and bandpass filters.
This microcircuit has a low power requirement of 3.0
volts (min.) and is encapsulated in either 16-pin DIL or
small outline SMD (S.O.I.C.) plastic packages both of
which are of a physical size suitable for either base or
handset type telephone instruments as well as battery-
portable and mobile communications systems.
Pin Number
FX118DW
FX118P
1
Xtal:
Output of clock oscillator inverter.
Function
2
No Internal Connection: It is recommended that, to improve noise conditions, this pin is connected to V
SS
.
3
LPF(1) Out:
The output of the Channel 1 Lowpass Filter. It is to be coupled to “B Mod(1) In” via a 1.0µF
capacitor – see Figure 2.
4
B Mod(1) In:
The input to Channel 1 balanced modulator. Internally biased at V
DD
/2 it is to be coupled to
“LPF(1)” via a 1.0µF capacitor – see Figure 2.
5
V
SS
:
Negative supply (GND).
6
C1 Out:
The analogue output of Channel 1.
7
C1 Amp Output:
Channel 1 amplifier with external components (see Figure 2) can be used to provide gain in
the signal path.
8
C1 In:
The negative input of Channel 1 Amplifier. Recommended external components are shown in Figure 2.
9
C2 In:
The negative input of Channel 2 Amplifier. Recommended external components are shown in Figure 2.
10
C2 Amp Output:
Channel 2 amplifier with external components (see Figure 2) can be used to provide gain in
the signal path.
11
C2 Out:
The analogue output of Channel 2.
12
V
BIAS
:
The internal analogue bias line at V
DD
/2. It should be decoupled to V
SS
via a 1.0µF or greater capacitor.
See Figure 2.
13
B Mod(2) In:
The input to Channel 2 balanced modulator. Internally biased at V
DD
/2 it is to be coupled to
“LPF(2)” via a 1.0µF capacitor – see Figure 2.
14
LPF(2) Out:
The output of the Channel 2 Lowpass Filter. It is to be coupled to “B Mod(2) In” via a 1.0µF
capacitor – see Figure 2.
15
V
DD
:
The positive supply rail. A single positive supply voltage (3.0v – 5.0v) is required. Levels and voltages
within the Duplex Frequency Inverter are dependent upon this supply.
16
Xtal/Clock:
4.433619 MHz Xtal or externally derived clock is injected at this pin. See Figure 2. Operation of
the FX118 without a Xtal or clock input may cause device damage.
2
Application Information
V
DD
C
3
C
2
X
1
C
1
R
1
XTAL
1
2
16
15
14
13
XTAL/CLOCK
V
DD
LPF(2) OUT
B MOD(2) IN
LPF(1) OUT
3
4
C
4
B MOD(1) IN
C
8
V
SS
C1 OUT
CHANNEL 1 OUTPUT
CHANNEL 1 INPUT
C1 IN
FX118
5
6
7
8
12
11
10
9
V
BIAS
C
C2 OUT
C2 AMP OUT
V
SS
R
5
7
R
3
C1 AMP OUT
CHANNEL 2 OUTPUT
CHANNEL 2 INPUT
C2 IN
C
5
R
2
R
4
C
6
V
SS
Component
R
1
R
2
R
3
C
5
R
4
R
5
C
6
C
1
=
Value
1.0MΩ
See Note
See Note
47pF
C
2
C
3
C
4
=
33pF
0.47µF
1.0µF
C
7
C
8
X
1
=
1.0µF
1.0µF
4.433619MHz
T
olerances
C =
±
20% R =
±
10%
NOTES
1. Configurations R
2
, R
3
, C
5
and R
4
, R
5
, C
6
should be chosen with respect to the specific application.
2. Operation of any CML microcircuit without a Xtal or clock input may cause device damage. To minimise damage
in the event of a Xtal/drive failure, it is recommended that the power rail (V
DD
) is fitted with a current limiting
device (resistor or fast-reaction fuse).
Fig.2 Recommended External Components
Rx Channel
RF
AMP
IF
AMP
DETECTION
BASE UNIT
FX118
DE-EMPHASIS
AF AMP
FM
CHANNEL 1 (C1)
RF
AMP
PRE-
EMPHASIS
CHANNEL 2 (C2)
FM
HYBRID
TRANSFORMER
AF AMP
TELEPHONE
LINE
MODULATION
Tx Channel
Rx Channel
RF
AMP
IF
AMP
DETECTION
FX118
DE-EMPHASIS
AF AMP
FM
CHANNEL 1 (C1)
RF
AMP
PRE-
EMPHASIS
CHANNEL 2 (C2)
FM
AF AMP
MODULATION
Tx Channel
HANDHELD UNIT
Fig.3 Example of the FX118 Employed in a Cordless Telephone Application
3
Application Information ......
+5
0
-3
Gain
dB
-10
Audio Input Level = 275mVrms
V
DD
= 3.75V
-20
-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)
A
B
C
Input Voiceband Frequencies
Lowpass Filtered Voiceband
for Input to
Balanced Modulator
D
Speech Band
0
1000Hz
2000Hz
3000Hz
(3)
Carrier Frequency (3300Hz)
Generated On-Chip for Input to
Balanced Modulator
(4)
C
D
B
A
Bandpass Filtered Voiceband
Presented at the Ouput
after Mixing with the Carrier Frequency
in the Balanced Modulator
0
1000
2000
3000
0
1000
2000
3000 3300
Fig.5 A Pictorial Explanation of the FX118 “Scramble Operation”
4
Specification
Absolute Maximum Ratings
Exceeding the maximum rating can result in device damage. Operation of the device outside the operating limits is not
implied.
Supply voltage
Input voltage at any pin (ref V
SS
= 0V)
Sink/source current (supply pins)
(other pins)
Total device dissipation @ T
AMB
25°C
Derating
Operating temperature range:
Storage temperature range:
Operating Limits
All device characteristics are measured under the following conditions unless otherwise specified:
V
DD
= 3.75V. T
AMB
= 25°C. Xtal/Clock f
0
= 4.433619MHz. Audio level 0dB ref: = 388mV rms @ 1.0kHz.
Characteristics
See Note
Min.
3.0
–
1.0
–
–
–
10.0
–
–
–
-16.0
–
–
–
–
–
–
–
Typ.
3.75
4.0
10.0
2.0
200
10.0
–
10.0
10.0
10.0
–
30.0
-40.0
-55.0
-40.0
3299
-42.0
-46.0
Max.
5.5
6.0
–
–
–
–
–
–
–
–
4.0
–
–
–
–
–
–
–
Unit
V
mA
MΩ
kΩ
Ω
kΩ
MΩ
kΩ
V/V
MHz
dB
dB
dB
dB
dB
Hz
dB
dBp
FX118DW/P
FX118DW/P
-0.3 to 7.0V
-0.3 to (V
DD
+ 0.3V)
+/- 30mA
+/- 20mA
800mW Max.
10mW/°C
-40°C to +85°C
-40°C to +85°C
Static Values
Supply Voltage
Supply Current
Input Impedance
(Amplifiers)
Output Impedance
(LP Filters)
Output Impedance
(C1, C2 )
Output Impedance
(C1, C2 Amps)
On-Chip Xtal Oscillator
R
IN
R
OUT
Inverter Gain
Gain/Bandwidth Product
Dynamic Values
Analogue Signal Input Levels
SINAD
6
Unwanted Modulation Products
1, 2
Carrier Breakthrough
1, 2
Baseband Breakthrough
1, 2
Carrier Frequency
Analogue Output Noise
3
Analogue Output Noise
5
Filters
Input Lowpass Filter
1
Cut-Off Frequency (-3dB)
Passband Ripple (300Hz - 3kHz)
Attenuation at 3.3kHz
Attenuation at 3.6kHz
Passband Gain
Output Bandpass Filter
1, 4
Passband Frequencies
Passband Ripple
Low Freq. Roll-Off <200Hz
High Freq. – Attenuation at 3.4kHz
Passband Gain
Overall Modulated and De-Modulated Channel Response
Passband Frequencies (Tx and Rx Channel)
Passband Ripple
Low Freq. Roll-Off <250Hz
High Freq. – Attenuation at 3.4kHz
Passband Gain
4
Distortion
1
Notes:
1.
2.
3.
4.
5.
6.
–
–
–
–
–
300
–
12.0
–
3.5
300
-3.0
18.0
–
–
–
3100
±1.0
30.0
45.0
0.5
–
±1.0
–
48.0
4.5
–
–
–
48.0
0.5
3.0
–
–
–
–
–
3000
–
–
–
5.5
3000
2.0
–
–
–
–
Hz
dB
dB
dB
dB
Hz
dB
dB/oct.
dB
dB
Hz
dB
dB/oct.
dB
dB
%
Measured with an audio input level of -3.0dB.
With respect to a single modulated (scrambling) channel.
Measured with a short circuit input, at any analogue output, in a 30.0kHz bandwidth.
With Input Amplifier gain at 0dB.
Measured psophometrically weighted, at any analogue output.
Measured in a 30kHz bandwidth.
5
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