t4225b ATMEL Corporation, t4225b Datasheet - Page 3

• Manufacturer Part Number: t4225b
• Description: Low-cost Time-code Receiver
• Manufacturer: ATMEL Corporation

Rev. A3, 03-Dec-98
IN
A ferrite antenna is connected between IN and VCC. For
high sensitivity, the Q factor of the antenna circuit should
be as high as possible. Please note that a high Q factor
requires temperature compensation of the resonant
frequency in most cases. We recommend a Q factor
between 50 and 100. Specifications are valid for Q > 30.
An optimal signal-to-noise ratio will be achieved by a
resonant resistance of 50 to 200 k
SB
A resistor R
trols the bandwidth of the crystal filters. It is recom-
mended: R
60 kHz WWVB and R
Q1A, Q1B
In order to achieve a high selectivity, a crystal is con-
nected between the Pins Q1A and Q1B. It is used with the
serial resonant frequency of the time-code transmitter
(e.g., 60 kHz WWVB, 77.5 kHz DCF or 40 kHz JG2AS).
The equivalent parallel capacitor of the filter crystal is
internally compensated. The compensated value is about
0.7 pF. If full sensitivity and selectivity are not needed,
the crystal filter can be substituted by a capacitor of 10 pF
for DCF and WWVB and 22 pF for JG2AS.
94 8382
SB
SB
VCC
Q1A
= 0
IN
is connected between SB and GND. It con-
W
for DCF 77.5 kHz, R
SB
Figure 3.
Figure 4.
Figure 5.
= open for JG2AS 40 kHz.
W
.
GND
Q1B
GND
SB
SB
94 8379
94 8381
= 10 k
W
for
REC
Rectifier output and integrator input: The capacitor C
between REC and INT is the lowpass filter of the rectifier
and at the same time a damping element of the gain
control.
DEC
Decoder input: Senses the current through the integration
capacitor C
about 420 k
C
SL
AGC hold mode: SL high (V
function, SL low (V
holds the voltage V
the AGC amplifier gain.
2
.
94 8378
94 8376
2
W
. The dynamic input resistance has a value of
and is low compared to the impedance of
DEC
VCC
SL
INT
SL
= 0) disconnects the rectifier and
Figure 6.
Figure 7.
Figure 8.
at the integrator output and also
SL
= V
T4225B
GND
REC
GND
CC
) sets normal
94 8374
3 (16)
1