DA6179.000
22 January, 2007
TYPICAL APPLICATION (Continued)
Note 1: Crystals
The crystals as well as ferrite antenna frequencies are chosen according to the time signal system (Table 2).
The reason why the crystal frequency is about 3 Hz higher than the signal frequency is that the crystal is
operated without the loading capacitor. Without loading capacitor the actual resonance frequency is about 3 Hz
lower thus 77.503 kHz crystal resonates at 77.500 kHz when no loading capacitor is used.
Table 2. Time Signal System Frequencies
Location
Time Signal System
Antenna Frequency Recommended Crystal Frequency
DCF77
HBG
MSF
WWVB
JJY
BPC
Germany
Switzerland
United Kingdom
USA
Japan
China
77.5 kHz
75 kHz
60 kHz
60 kHz
40 kHz and 60 kHz
68.5 kHz
77.503 kHz
75.003 kHz
60.003 kHz
60.003 kHz
40.003 kHz and 60.003 kHz
68.505 kHz
The crystal shunt capacitance C0 should be matched as well as possible with the internal shunt capacitance
compensation capacitor CC of MAS6179. See Compensation Capacitance Options in table 3.
Table 3. Compensation Capacitance Options
CC
Device
Crystal Description
MAS6179A1
MAS6179A2
0.75 pF
1.3 pF
For low C0 crystal
For high C0 crystal
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 1pF floating package shunt capacitance can have
0.85pF 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.
Highest frequency crystal is connected to crystal output pin 1 (QO1). Medium frequency crystal is connected to
crystal output pin 2 (QO2). Lowest frequency crystal is connected to crystal output pin 3 (QO3). The other pin of
each crystal is connected to common crystal input pin QI.
Table 4 below presents some crystal manufacturers having suitable crystals for time signal receiver application.
Table 4. Crystal Manufacturers and Crystal Types in Alphabetical Order for Time Signal Receiver Application
Dimensions
Manufacturer
Crystal Type
Web Link
Citizen
Epson
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/
KDS Daishinku
Microcrystal
http://www.kds.info/index_en.htm
http://www.microcrystal.com/
Seiko
Instruments
http://www.sii-crystal.com
Note 2: AGC Capacitor
The AGC and DEC capacitors must have low leakage currents due to very small signal currents through the
capacitors. The insulation resistance of these capacitors should be at minimum 100 MΩ. Also probes with at
least 100 MΩ impedance should be used for voltage probing of AGC and DEC pins. Electrolytic AGC capacitor
should have voltage rating at least 25 V for low enough leakage. DEC capacitor can be low leakage chip
capacitor.
7 (10)
MAS [ MICRO ANALOG SYSTEMS ]
