DA6180.001
27 December, 2006
TYPICAL APPLICATION (Continued)
Note 1: Crystals
The crystal as well as ferrite antenna frequencies are chosen according to the time-signal system (Table 1). The
crystal shunt capacitance C
0
should be matched as well as possible with the internal shunt capacitance
compensation capacitor C
C
of MAS6180. MAS6180A5 is option for external crystal compensation capacitor. The
external compensation capacitor should be matched similarly as well as possible with crystal’s shunt
capacitance. See Compensation Capacitance Options on table 2.
Table 1.
Time-Signal System Frequencies
Time-Signal System
Location
DCF77
HGB
MSF
WWVB
JJY
BPC
Germany
Switzerland
United Kingdom
USA
Japan
China
Antenna Frequency
77.5 kHz
75 kHz
60 kHz
60 kHz
40 kHz and 60 kHz
68.5 kHz
Recommended Crystal Frequency
77.503 kHz
75.003 kHz
60.003 kHz
60.003 kHz
40.003 kHz and 60.003 kHz
68.505 kHz
Table 2 .
Compensation Capacitance Options
Crystal Description
Device
C
C
MAS6180A1
MAS6180A2
MAS6180A5
0.75 pF
1.3 pF
C
C_EXT
For low C
0
crystals
For high C
0
crystals
For any crystals, external compensation capacitor
It should be noted that grounded crystal package has reduced shunt capacitance. This value is about 85% of
floating crystal shunt capacitance. For example crystal with 1 pF floating package shunt capacitance can have
0.85 pF grounded package shunt capacitance. PCB traces of crystal and external compensation capacitance
should be kept at minimum to minimize additional parasitic capacitance which can cause capacitance
mismatching.
In dual band receiver configuration the crystals can be connected in parallel thus external compensation
capacitor value C
C_EXT
must be sum of two crystals’ shunt capacitances. Instead of parallel crystal connection it is
also possible to connect other crystal from QOP pin and the other crystal from QOM pin to common QI pin (figure
3). In this circuit configuration no external compensation capacitor is required since the crystals compensate
each other. The sensitivity of dual band receiver configuration will be lower than that of single band receiver
configuration since the noise band width of crystal filter with two parallel crystals is double.
Table 3 below presents some crystal manufacturers having suitable crystals for timesignal receiver application.
Table 3.
Crystal Manufacturers and Crystal Types in Alphaphetical Order for Timesignal Receiver Application
Manufacturer
Crystal Type
Dimensions
Web Link
Citizen
Epson Toyocom
KDS Daishinku
Microcrystal
Seiko
Instruments
CFV-206
C-2-Type
C-4-Type
DT-261
MX1V-L2N
MX1V-T1K
VTC-120
ø 2.0 x 6.0
ø 1.5 x 5.0
ø 2.0 x 6.0
ø 2.0 x 6.0
ø 2.0 x 6.0
ø 2.0 x 8.1
ø 1.2 x 4.7
http://www.citizen.co.jp/tokuhan/quartz/
http://www.epsontoyocom.co.jp/english/
http://www.kds.info/index_en.htm
http://www.microcrystal.com/
http://www.sii-crystal.com
6 (9)
MAS [ MICRO ANALOG SYSTEMS ]
