U4221B
Radio Controlled Clock Receiver
Description
The U4221B is a bipolar integrated straight through receiver circuit in the frequency range of 60 to 80 kHz. The device
is designed for radio controlled clock application.
Features
D
Low power consumption
D
Very high sensitivity
D
High selectivity by quartz resonator
D
Stop-function available
D
Only a few external components necessary
D
Digitized serial output signal
Block Diagram
PON
14
TCO
13
FSI
12
NC
10
VCCD
9
VCCA
16
Power supply
Driver
Comparator
FSS
11
GND
15
AGC
CAGC
4
IN2
1
IN1
2
Amplifier 1
Amplifier 2
Demodulator
3
GND (analog)
8
OUTA1
6
INA2
Figure 1.
7
GND (digital)
5
CDEM
93 7506 e
TELEFUNKEN Semiconductors
Rev. A1, 15-May-96
1 (12)
Preliminary Information
U4221B
Pin Description
Pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Symbol
IN2
IN1
GND
CAGC
CDEM
INA2
GND
OUTA1
V
CCD
NC
FSS
FSI
TCO
PON
GND
V
CCA
Function
Amplifier 1 - Input 2
Amplifier 1 - Input 1
Analog ground
Time constant of AGC
Low pass filter
Amplifier 2 input
Digital ground
Amplifier 1 output
Supply voltage (digital)
Not connected
Field strength select
Field strength indication
Time code output
Power ON/OFF control
Ground (substrate)
Supply voltage (analog)
IN2
1
16
VCCA
IN1
2
15
GND
GND
3
14
PON
CAGC
4
13 TCO
U 4221 B
CDEM
5
12
FSI
INA2
6
11
FSS
GND
7
10
NC
OUTA1
8
93 7507 e
9
VCCD
IN1, IN2
IN2 is connected to Pin 16 (V
CCA
). A ferrite antenna is
connected between IN1 and IN2. Q of antenna circuit
should be as high as possible, but the temperature
influence must be compensated. The resonant resistance
should be 200 k
W
to 300 k
W
for optimal sensitivity.
CDEM
After demodulation the signal is low pass filtered by the
capacitor CDEM.
PON
If PON is connected to V
CCD,
the U4221B receiver IC
will be activated. The set-up time is typical 2.5 s after ap-
plying V
CCD
at this pin. If PON is connected to GND, the
receiver will go into stop mode.
OUTA1, INA2
To achieve a high selectivity, a quartz resonator is
connected between the pins OUTA1 and INA2. It is used
with the serial resonance frequency of the time code
transmitter (e.g. 60 kHz WWVB, 77.5 kHz DCF). The
parasitic parallel capacitance C
0
of the quartz resonator
should be 0.5 pF to 1 pF.
FSS
This pin is connected to GND, otherwise the field strength
indication FSI is disabled.
CAGC
A control voltage derived from the field strength is
generated to control the amplifiers. The time constant of
this automatic gain control (AGC) is influenced by the
capacitor CAGC.
FSI
If the voltage at the input of amplifier 1 is higher than
about 5
m
V, FSI will be high.
2 (12)
Preliminary Information
TELEFUNKEN Semiconductors
Rev. A1, 15-May-96
U4221B
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 current source and a NPN
switching transistor T
S
. The guaranteed source output
current is 0.2
µA
(TCO = high) and the sink current is
1
µA
(TCO = low). Considering these output currents, the
supply voltage and the switching levels of the following
µC,
the lowest load resistance is defined. The maximum
load capacitance is 100 pF.
In order to improve the driving capability an external
pull-up resistor can be used. The value of the resistor
should be 4.7 M
W
. To prevent an undefined output vol-
tage in the power-down state of the U4221B, the use of
this pull-up resistor is recommended.
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 2). Using a CMOS driver this circuit must be
connected to V
CCD
.
pin 9
V
CCD
I
SOURCE
0.2
m
A
TS
pin13
TCO
93 7689 e
Condition for signal reception:
S/N
≈
4 at comparator input.
Important parameters are:
V
NA
= (4 k T R
res
)
1/2
BW
A
= f
res
/Q
A
input noise voltage density of preamplifier:
V
NA1
: 40 nV/Hz
1/2
(typ)
bandwidth of preamplifier:
BW
A1
: 60 kHz (typ)
bandwidth of crystal filter:
BW
CF
: 16 Hz (typ)
ultimate attenuation of crystal filter:
D
CF
: –35 dB (typ)
whereas:
V
NA
k
T
BW
A
f
res
Q
A
antenna noise voltage density
1.38 10
–23
Ws/K (Boltzmann constant)
absolute temperature
bandwidth of antenna
resonant frequency
Q antenna
@
4.7 M
W
100 k
W
TCO
The equivalent input noise voltage at the preamplifier in-
put is:
I
SINK
1
m
A
V
N
Figure 2.
+
V
NA
@
2
BW
CF
)
2
V
NA
@
2
BW
A
D
CF
) @@
2
Functional Description
The following description gives you some additional
information and hints in order to facilitate your design, in
particular the problems of the antenna.
Figure 3 shows the principal function of the receiver
(simplified consideration).
Rres
CF
A1
A 2 and
Demodulator
Comparator
93 7521 e
@@@)
V
@
NA1
BW
CF
)
V
NA1
@
BW
A1
D
CF
whereas:
R
res
= 300 k
W
, BW
A
= 1 kHz then V
N
≈
0.4
m
V
The condition for signal reception is:
S/N
≈
4
⇒
sensitivity
≈
1.6
m
V
That means that the noise voltage of antenna within the
bandwidth of the crystal filter dominates and the
bandwidth of antenna is uncritical for the sensitivity
aspect.
Figure 3.
R
res
: resonant resistance, A1: preamplifier,
A2: amplifier 2, CF: crystal filter
TELEFUNKEN Semiconductors
Rev. A1, 15-May-96
3 (12)
Preliminary Information
U4221B
There is some consideration concerning the calculation of
R
res
:
in order to achieve high signal voltage:
R
res
should be high
in order to achieve low antenna noise voltage:
R
res
should be low
R
res
< 200 k
W
:
the input noise voltage of A 1 dominates
R
res
> 300 k
W
:
the antenna noise voltage dominates
That means the resonant resistance should be between
200 k
W
and 300 k
W.
Q of antenna must be high for attenuation of interfering
signals. But the temperature must not influence the
resonance frequency.
it is easy to compute the resonance resistance according
to the following formula:
R
res
1
+
2
@ @
BW
@
C
p
A
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 dis-
tinguished by the simple DC-resistance of the wire. Skin
effects can be observed but do not dominate.
Therefore it should be no problem to achieve the
recommended 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
compensation 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
capacitors for specified values of temperature coefficient.
Furthermore some critical parasitics have to be
considered. 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 capac-
itor 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.
For the adjustment of the resonance frequency the
capacitance of the probe and the input capacitance of the
IC are to be taken into account. The alignment should be
done in the final environment. The bandwidth is so low
that metal parts close to the antenna influence the
resonance frequency. The adjustment can be done by
pushing the coil along the bar antenna.
Design Hints for the Ferrite Antenna
The bar antenna is the most 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 200 k
W
to 300 k
W
. 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.
RF - Signal
generator
77.5 kHz
Scope
w
wire loop
C
res
Probe
10 : 1
10 M
W
94 7907 e
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,
4 (12)
Preliminary Information
TELEFUNKEN Semiconductors
Rev. A1, 15-May-96
U4221B
Absolute Maximum Ratings
Parameters
Supply voltage
Ambient temperature range
Storage temperature range
Junction temperature
Electrostatic handling
( MIL Standard 883°C)
Symbol
V
CC
T
amb
R
stg
T
j
±
V
ESD
Value
5.5
–20 to +70
–30 to +85
125
2000
Unit
V
_
C
_
C
_
C
V
Thermal Resistance
Parameters
Thermal resistance
Symbol
R
thJA
Value
70
Unit
K/W
Electrical Characteristics
V
CCA
, V
CCD
= 3.0 V, reference point Pins 3, 7, 15, input signal according to DCF 77 transmitter, T
amb
= 25
_
C,
unless otherwise specified
Parameters
Supply voltage range
Supply current
I
CC
= I
CCA
+ I
CCD
Test Conditions / Pins
Pins 9, 16
Pins 9, 16
without reception signal
with reception signal >
20
m
V OFF-mode
R
gen
= 50
W
Pins 1,2
R
res
300 k
W
, Q
res
> 30
R
gen
= 50
W
Pins 1,2
R
res
300 k
W
, Q
res
> 30
Pins 1, 2
Symbol
V
CCA
V
CCD
I
CC
Min.
2.4
Typ.
Max.
5.5
Unit
V
Reception frequency range
Minimum input voltage
Maximum input voltage
Input capacitances to
ground
Set-up time after POWER
ON
TIMING CODE OUTPUT; TCO
Pin 13
Output voltage
R
LOAD
= 13 M
W
to GND
HIGH
R
LOAD
= 2.6 M
W
to V
CCD
LOW
Output current
V
TCO
= V
CCD/2
HIGH
V
TCO
= V
CCD/2
LOW
Decoding characteristics
input carrier reduction
100 ms input carrier
reduction 200 ms
POWER ON/OFF CONTROL; PON Pin 14
Input voltage
Generator output resistance
HIGH
200 k
W
LOW
v
v
f
in
V
in
V
in
C
in 1
C
in 2
t
pon
60
1.5
40
1
1
2.5
40
35
0.2
80
1.75
m
A
m
A
m
A
kHz
m
V
mV
pF
5
s
V
OH
V
OL
I
SOURCE
I
SINK
t
100
t
200
V
CCD
-0.4
0.4
0.2
1
50
150
0.4
4
110
230
V
V
mA
mA
ms
ms
v
V
CCD
–0.4
0.4
V
V
TELEFUNKEN Semiconductors
Rev. A1, 15-May-96
5 (12)
Preliminary Information
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