MAS9178A1TC00.01 参数 Datasheet PDF下载

DA9178.001

10 Dec, 2003

TYPICAL APPLICATION (Continued)

Note 1

Note 4

Optional

Control

for AGC on/hold

QI

QOM

AON

Demodulator

&

Comparator

OUT

Receiver

Output

QOP

RFP

Ferrite

Antenna

AGC Amplifier

RFM

Antenna

Frequency

Selection

Power Supply/Biasing

VDD

1.4 V

VSS

PDN

AGC

C

AGC

+

10

µF

DEC

C

DEC

47 nF

Figure 3

Note 3

Note 2

Power Down /

Fast Startup

Control

Dual band application circuit of external compensation capacitance version MAS9178A5.

Note 1: Crystal

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

=0.875 pF of MAS9178A1. External compensation pad QOM is unconnected in

MAS9178A1. MAS9178A5 does not have internal compensation capacitance C

C

and it requires use of external

compensation capacitor C

C_EXT

. It must be connected between pins QOM and QI (see figure 2). C

C_EXT

should

have equal value with crystal’s effective shunt capacitance C

0

. External compensation version MAS9178A5

should be used when fixed 0.875 pF compensation capacitance of MAS9178A1 does not match well with used

crystal’s shunt capacitance.

It should be noted that grounded crystal package has reduced shunt capacitance. This value is about 85% of

floating crystal 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.

Time-Signal System

DCF77

MSF

WWVB

JJY

Table 1

Location

Antenna Frequency

Recommended Crystal Frequency

77.503 kHz

60.003 kHz

60.003 kHz

40.003 kHz and 60.003 kHz

Germany

77.5 kHz

United Kingdom

60 kHz

USA

60 kHz

Japan

40 kHz and 60 kHz

Time-Signal System Frequencies

5 (8)