U4224B
TELEFUNKEN Semiconductors
Rev. A3, 02-Apr-96
1 (17)
Time Code Receiver
Description
The U4224B is a bipolar integrated straight through receiver circuit in the frequency range of 40 to 80 kHz.
The device is designed for radio controlled clock applications.
Features
D Very low power consumption
D Very high sensitivity
D High selectivity by using two crystal filters
D Power down mode available
D Only a few external components necessary
D Digitalized serial output signal
D AGC hold mode
Block Diagram
Power Supply
Decoder
AGC
Amplifier
PON
DEC
SB
V
CC
GND
93 7727 e
TCO
15
16
11
10
9
12
FLB
FLA
SL
4
5
6
13
14
7
8
Q1A
Q1B Q2A
Q2B
REC
INT
1
3
2
IN
Rectifier &
Integrator
U4224B
TELEFUNKEN Semiconductors
Rev. A3, 02-Apr-96
2 (17)
Pin Description
Pin
Symbol
Function
SO 16 L
1
V
CC
Supply voltage
2
IN
Amplifier Input
3
GND
Ground
4
SB
Bandwidth control
5
Q1A
Crystal filter 1
6
Q1B
Crystal filter 1
7
REC
Rectifier output
8
INT
Integrator output
9
DEC
Decoder input
10
FLA
Low pass filter
11
FLB
Low pass filter
12
SL
AGC hold mode
13
Q2A
Crystal filter 2
14
Q2B
Crystal filter 2
15
PON
Power ON/OFF control
16
TCO
Time code output
3
4
5
2
1
6
7
8
V
CC
IN
GND
SB
TCO
PON
15
14
16
13
12
11
10
9
DEC
93 7729 e
U4224B
Q1A
Q1B
REC
INT
Q2B
Q2A
SL
FLB
FLA
IN
A ferrite antenna is connected between IN and V
CC
. For
high sensitivity the Q of the antenna circuit should be as
high as possible, but a high Q often requires temperature
compensation of the resonant frequency. Specifications
are valid for Q > 30. An optimal signal to noise ratio will
be achieved by a resonant resistance of 50 to 200 k
W.
IN
V
CC
94 8379
SB
A resistor R
SB
is connected between SB and GND. It con-
trols the bandwidth of the crystal filters. It is
recommended: R
SB
= 0
W for DCF 77.5 kHz, R
SB
=
10 k
W for 60 kHz WWVB and R
SB
= open for JG2AS
40 kHz.
SB
GND
94 8381
U4224B
TELEFUNKEN Semiconductors
Rev. A3, 02-Apr-96
3 (17)
Q1A, Q1B
In order to achieve a high selectivity, a crystal is con-
nected between the pins Q1A
and Q1B. It is used with the
serial resonance frequency of the time code transmitter
(e.g. 60 kHz WWVB, 77.5 kHz DCF or 40kHz JG2AS).
The equivalent parallel capacitor of the filter crystal is
internally compensated. The compensated value is about
0.7 pF. If the full sensitivity and selectivity is not needed,
the crystal filter can be substituted by a capacitor of 10 pF
for DCF and WWVB and 22 pF for JG2AS.
Q1A
Q1B
94 8382
GND
REC
Rectifier output and integrator input: The capacitor C1
between REC and INT is the lowpass filter of the rectifier
and at the same time a damping element of the gain
control.
REC
GND
94 8374
DEC
Decoder input: Senses the current through the integration
capacitor C2. The dynamic input resistance has a value of
about 420k
W and is low compared to the impedance of
C2.
DEC
GND
94 8376
SL
AGC hold mode: SL high (V
SL
= V
CC
) sets normal func-
tion, SL low (V
SL
= 0) disconnects the rectifier and holds
the voltage V
INT
at the integrator output and also the AGC
amplifier gain.
V
CC
SL
94 8378
INT
Integrator output: The voltage V
INT
is the control voltage
for the AGC. The capacitor C2 between INT and DEC
defines the time constant of the integrator. The current
through the capacitor is the input signal of the decoder.
INT
GND
94 8375
FLA, FLB
Lowpass filter: A capacitor C3 connected between FLA
and FLB supresses higher frequencies at the trigger
circuit of the decoder.
FLB
FLB
94 8377
U4224B
TELEFUNKEN Semiconductors
Rev. A3, 02-Apr-96
4 (17)
Q2A, Q2B
According to Q1A, Q1B a crystal is connected between
the pins Q2A and Q2B. It is used with the serial resonance
frequency of the time code transmitter (e.g. 60 kHz
WWVB, 77.5 kHz DCF or 40 kHz JG2AS). The equi-
valent parallel capacitor of the filter crystal is internally
compensated. The value of the compensation is about
0.7 pF.
Q2A
Q2B
94 8383
GND
PON
If PON is connected to GND
,
the U 4224 B receiver IC
will be activated. The set-up time is typical 0.5s after
applying GND at this pin. If PON is connected to V
CC
, the
receiver will go into power down mode.
V
CC
PON
94 8373
TCO
The digitized serial signal of the time code transmitter can
be directly decoded by a microcomputer. Details about
the time code format of several transmitters are described
separately.
The output consists of a PNP
*NPN push-pull-stage. It
should be taken into account that in the power down mode
(PON = high) TCO will be high.
V
CC
TCO
GND
PON
94 8380
An additional improvement of the driving capability may
be achieved by using a CMOS driver circuit or a NPN
transistor with pull-up resistor connected to the collector
(see figure KEIN MERKER). Using a CMOS driver this
circuit must be connected to V
CC
.
10 k
W
V
CC
pin16
TCO
TCO
94 8395 e
100 k
W
Figure 1.
Please note:
The signals and voltages at the pins REC, INT, FLA, FLB,
Q1A, Q1B, Q2A and Q2B cannot be measured by stan-
dard measurement equipment due to very high internal
impedances. For the same reason the PCB should be pro-
tected against surface humidity.
Design Hints for the Ferrite Antenna
The bar antenna is a very critical device of the complete
clock receiver. But by observing some basic RF design
knowledge, no problem should arise with this part. The IC
requires a resonance resistance of 50 k
W to 200 kW. This
can be achieved by a variation of the L/C-relation in the
antenna circuit. But it is not easy to measure such high
resistances in the RF region. It is much more convenient
to distinguish the bandwidth of the antenna circuit and
afterwards to calculate the resonance resistance.
Thus the first step in designing the antenna circuit is to
measure the bandwidth. Figure 4 shows an example for
the test circuit. The RF signal is coupled into the bar
antenna by inductive means, e.g. a wire loop. It can be
measured by a simple oscilloscope using the 10:1 probe.
The input capacitance of the probe, typically about 10 pF,
should be taken into consideration. By varying the
frequency of the signal generator, the resonance
frequency can be determined.
Scope
RF - Signal
generator
77.5 kHz
C
res
Probe
10 : 1
wire loop
94 7907 e
w10 MW
U4224B
TELEFUNKEN Semiconductors
Rev. A3, 02-Apr-96
5 (17)
Afterwards, the two frequencies where the voltage of the
rf signal at the probe drops 3 dB down can be measured.
The difference between these two frequencies is called
the bandwidth BW
A
of the antenna circuit. As the value
of the capacitor C
res
in the antenna circuit is well known,
it is easy to compute the resonance resistance according
to the following formula:
R
res
+
1
2
@ p @ BW
A
@ C
res
whereas
R
res
is the resonance resistance,
BW
A
is the measured bandwidth (in Hz)
C
res
is the value of the capacitor in the antenna circuit
(in Farad)
If high inductance values and low capacitor values are
used, the additional parasitic capacitances of the coil
must be considered. It may reach up to about 20 pF. The
Q-value of the capacitor should be no problem if a high
Q-type is used. The Q-value of the coil is more or less
distinguished by the simple DC-resistance of the wire.
Skin effects can be observed but do not dominate.
Therefore it shouldn't be a problem to achieve the recom-
mended values of resonance resistance. The use of thicker
wire increases Q and accordingly reduces bandwidth.
This is advantageous in order to improve reception in
noisy areas. On the other hand, temperature compen-
sation of the resonance frequency might become a
problem if the bandwidth of the antenna circuit is low
compared to the temperature variation of the resonance
frequency. Of course, Q can also be reduced by a parallel
resistor.
Temperature compensation of the resonance frequency is
a must if the clock is used at different temperatures.
Please ask your dealer of bar antenna material and of ca-
pacitors for specified values of temperature coefficient.
Furthermore some critical parasitics have to be consid-
ered. These are shortened loops (e.g. in the ground line of
the PCB board) close to the antenna and undesired loops
in the antenna circuit. Shortened loops decrease Q of the
circuit. They have the same effect like conducting plates
close to the antenna. To avoid undesired loops in the
antenna circuit it is recommended to mount the capacitor
C
res
as close as possible to the antenna coil or to use a
twisted wire for the antenna coil connection. This twisted
line is also necessary to reduce feedback of noise from the
microprocessor to the IC input. Long connection lines
must be shielded.
A final adjustment of the time code receiver can be done
by pushing the coil along the bar antenna. The maximum
of the integrator output voltage V
INT
at pin INT indicates
the resonant point. But attention: The load current should
not exceed 1 nA, that means an input resistance
w 1 GW
of the measuring device is required. Therefore a special
DVM or an isolation amplifier is necessary.
Absolute Maximum Ratings
Parameters
Symbol
Value
Unit
Supply voltage
V
CC
5.25
V
Ambient temperature range
T
amb
25 to +75
_C
Storage temperature range
R
stg
40 to +85
_C
Junction temperature
T
j
125
_C
Electrostatic handling
( MIL Standard 883 D ), excepted pins 5, 6, 13 and 14
V
ESD
2000
V
Thermal Resistance
Parameters
Symbol
Value
Unit
Thermal resistance
R
thJA
70
K/W
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