U4221B Datasheet, PDF (3/12 Pages) TEMIC Semiconductors – Radio Controlled Clock Receiver

U4221B
TCO
The digitized serial signal of the time code transmitter can
be directly decoded by a microcomputer. Details about
the time code format of several transmitters are described
separately.
The output consists of a PNP current source and a NPN
switching transistor T_S. The guaranteed source output
current is 0.2 µA (TCO = high) and the sink current is
1 µA (TCO = low). Considering these output currents, the
supply voltage and the switching levels of the following
µC, the lowest load resistance is defined. The maximum
load capacitance is 100 pF.
In order to improve the driving capability an external
W ^{pull-up resistor can be used. The value of the resistor}
should be 4.7 M . To prevent an undefined output vol-
tage in the power-down state of the U4221B, the use of
this pull-up resistor is recommended.
An additional improvement of the driving capability may
be achieved by using a CMOS driver circuit or a NPN
transistor with pull-up resistor connected to the collector
(see figure 2). Using a CMOS driver this circuit must be
connected to V_CCD.
pin 9
V_CCD
m ^ISOURCE
0.2 A
4.7 MW 100 kW
TCO
TS
m^ISINK
1A
pin13
TCO
93 7689 e
Figure 2.
Functional Description
The following description gives you some additional
information and hints in order to facilitate your design, in
particular the problems of the antenna.
Figure 3 shows the principal function of the receiver
(simplified consideration).
Rres
CF
A1
A 2 and
Demodulator
93 7521 e
Comparator
Figure 3.
R_res: resonant resistance, A1: preamplifier,
A2: amplifier 2, CF: crystal filter
Condition for signal reception:
S/N ≈ 4 at comparator input.
Important parameters are:
V_NA = (4 k T R_res)^1/2
BW_A = f_res/Q_A
input noise voltage density of preamplifier:
V_NA1: 40 nV/Hz^1/2 (typ)
bandwidth of preamplifier:
BW_A1: 60 kHz (typ)
bandwidth of crystal filter:
BW_CF: 16 Hz (typ)
ultimate attenuation of crystal filter:
D_CF: –35 dB (typ)
whereas:
@ ^{VNA antenna noise voltage density}
k 1.38 10^–23 Ws/K (Boltzmann constant)
T absolute temperature
BW_A bandwidth of antenna
f_res resonant frequency
Q_A Q antenna
+ _Ǹ^ǒ @ ^{Ǹ Ǔ} ) ǒ ^{@ Ǹ} Ǔ ) @@ ^{The equivalent input noise voltage at the preamplifier in-}
put is:
2
V_N
V_NA
2
BW _CF
V_NA BW_A
D_CF
ǒ Ǔ _{ǒ Ǔ @@@) @} Ǹ ₎ ^{@ Ǹ} _VNA1
2
BW_CF
2
V_NA1 BW_A1
D_CF
whereas:
W m R_res = 300 k , BW_A = 1 kHz then V_N ≈ 0.4 V
The condition for signal reception is:
m S/N ≈ 4 ⇒ sensitivity ≈ 1.6 V
That means that the noise voltage of antenna within the
bandwidth of the crystal filter dominates and the
bandwidth of antenna is uncritical for the sensitivity
aspect.
TELEFUNKEN Semiconductors
3 (12)
Rev. A1, 15-May-96
Preliminary Information