CME6005-TCSH C-Max, CME6005-TCSH Datasheet - Page 5

• Manufacturer Part Number: CME6005-TCSH
• Description: IC RECEIVER RC SSO16
• Manufacturer: C-Max

Specifications of CME6005-TCSH

• Frequency: 40kHz ~ 120kHz
• Sensitivity: -115dBm
• Modulation Or Protocol: UTC - Universal Time Code
• Applications: Radio Controlled Time
• Current - Receiving: 100µA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Voltage - Supply: 1.2 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Memory Size: -
• Data Rate - Maximum: -

7 Design Hints for the Ferrite Antenna
7.1 Dimensioning of antenna circuit for different clock/watch applications
The bar antenna is a very critical device of the complete clock receiver. Observing some basic RF design
rules helps to avoid possible problems. The IC requires a resonant resistance of 40 kΩ to 100 kΩ. This can
be achieved by a variation of the L/C-relation in the antenna circuit. In order to achieve this resonant
resistance, we recommend to use antenna capacitors of a value between 2.2nF and 6.8nF. The optimum
value of the capacitor has to be specified respecting the concrete application needs and different boundary
conditions(ferrite material, type of antenna wire, available space for antenna coil).It is not easy to measure
such high resistances in the RF region. A more convenient way is to distinguish between the different
bandwidths of the antenna circuit and to calculate the resonant resistance afterwards.
Thus, the first step in designing the antenna circuit is to measure the bandwidth. Figure 12 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 time signal
generator, the resonant frequency can be determined.
At the point where the voltage of the RF signal at the probe drops by 3 dB, the two frequencies can then be
measured. The difference between these two frequencies is called the bandwidth BW
As the value of the capacitor C
resistance according to the following formula:
R
Where
R
BW
C
If high inductance values and low capacitor values are used, the additional parasitic capacitance of the coil
must be considered. The Q value of the capacitor should be no problem if a high Q type is used. The Q
value of the coil differs more or less from the DC resistance of the wire. Skin effects can be observed but do
not dominate.
Therefore, it should not be a problem to achieve the recommended values of the resonant resistance. The
use of thicker wire increases the Q value and accordingly reduces bandwidth. This is advantageous in order
to improve reception in noisy areas. On the other hand temperature compensation of the resonant frequency
might become a problem if the bandwidth of the antenna circuit is low compared to the temperature variation
of the resonant frequency. Of course, the Q value can also be reduced by a parallel resistor.
Temperature compensation of the resonant frequency is a must if the clock is used at different temperatures.
Please ask your supplier of bar antenna material and of capacitors for specified values of the 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
Wire loop
res
res
res
CME6005
SPEC No.
= 2 x π X BW
A
is the resonant resistance,
is the value of the capacitor in the antenna circuit (Farad).
is the measured bandwidth
Time signal
generator
1
Time Solutions
A
X C
C
res
Revision
A.8
res
Figure 12.
res
04.12.06
Probe
10:1
State
in the antenna circuit is known, it is easy to compute the resonant
Scope
03.05.2007
C-MAX printed
Datasheet
English
Version
A
CME6005
of the antenna circuit.
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