U4224B Datasheet, PDF (5/17 Pages) TEMIC Semiconductors – Time Code Receiver

U4224B
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
2
p1
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
w W ^{the resonant point. But attention: The load current should}
not exceed 1 nA, that means an input resistance 1 G
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
± V_ESD
2000
V
( MIL Standard 883 D ), excepted pins 5, 6, 13 and 14
Thermal Resistance
Thermal resistance
Parameters
Symbol
R_thJA
Value
70
Unit
K/W
TELEFUNKEN Semiconductors
Rev. A3, 02-Apr-96
5 (17)