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DA6181B.002

5 May, 2011

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 than with load thus 77.503 kHz crystal resonates at 77.500 kHz when no loading capacitor is used.

Table 2. Time Signal System Frequencies

Time Signal System

Location

Antenna Frequency

Recommended Crystal Frequency

DCF77

Germany

77.5 kHz

77.503 Hz

HBG

Switzerland

75 kHz

75.003 kHz

MSF

United Kingdom

60 kHz

60.003 kHz

WWVB

USA

60 kHz

60.003 kHz

JJY

Japan

40 kHz and 60 kHz

40.003 kHz and 60.003 kHz

BPC

China

68.5 kHz

68.505 kHz

are used to cancel each other. Large shunt capacitance mismatch between the two crystals can lead to non-

ideal filter characteristics and wide noise band-width. Effectively this means lower sensitivity performance.

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.

When using MAS6181B1 it does not matter which of the two frequency crystals is connected to QO1 pin and

which to QO2 pin.

Table 3 below presents some crystal suppliers having suitable crystals for time signal receiver application.

Table 3. Crystal Suppliers and Crystal Types in Alphabetical Order for Time Signal Receiver Application

Supplier

Crystal Type

Dimensions

Web Link

Citizen

CFV-206

ø 2.0 x 6.0

http://www.citizen.co.jp/tokuhan/quartz/

Epson Toyocom

C-2-Type

C-4-Type

ø 1.5 x 5.0

ø 2.0 x 6.0

http://www.epsontoyocom.co.jp/english/

KDS Daishinku

DT-261

ø 2.0 x 6.0

http://www.kds.info/index_en.htm

Microcrystal

MS3V-T1R

1.45 x 1.45 x 6.7

http://www.microcrystal.com/

Seiko

Instruments

VTC-120

ø 1.2 x 4.7

http://www.sii-crystal.com

Note 2: AGC Capacitor

The 10µF AGC and 47nF 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 several 100 MΩ.

Also probes with at least several 100 MΩ impedance should be used for voltage probing of the AGC and DEC

pins to not disturb their operation. Tantalum capacitors have lower leakage than the electrolyte capacitors. In

case of using electrolyte type AGC capacitor the capacitor voltage rating should be at least 25 V for sufficiently

low leakage. The DEC capacitor can be low leakage chip capacitor since its capacitance value is small.

It is recommended to connect both AGC and DEC capacitors to VDD (see application figures 1 and 2) although

VSS connection is also possible. The VDD connection provides better supply noise immunity because the

signals and AGC gain are referenced to VDD. Additionally leakage currents are minimized in this connection

because in power down the AGC pin voltage is pulled to VDD (to minimum AGC gain) providing zero voltage

over the AGC capacitor.