12
LTC1540
sn1540 1540fas
LT/TP 0403 1K REV A • PRINTED IN USA
© LINEAR TECHNOLOGY CORPORATION 1997
TYPICAL APPLICATION
U
RF Field Detector
Figure 10 shows the complete circuit for a field detector
which was tested at 445MHz. A transmission line is used
to match the detector diode (1N5712) to a quarter-wave
whip antenna. The 0.23λ wavelength transmission line
section transforms the 1pF (350Ω) diode junction capaci-
tance to a virtual short at the base of the antenna. At the
same time it converts the received antenna current to a
voltage loop at the diode, giving excellent sensitivity.
Figure 10. Nanopower Field Detector
–
+
LTC1540
2V
TO 11V
2
1540 F10
10nF
0.23λ
1N5712
10nF
12M
180k
λ /4
10k
FB
7
6
5
8
3
4
1
Q
Q
CMOS
ONE SHOT
(CD4047)
PART NUMBER DESCRIPTION COMMENTS
LT
®
1178/LT1179 Dual/Quad 17µA Precision Single Supply Op Amps 70µV Max V
OS
, 5nA Max I
BIAS
LT1351 Single 250µA, 3MHz, 200V/µs Op Amp with Shutdown C-Load
TM
Op Amp Stable Driving Any Capacitive Load
LT1352/LT1353 Dual/Quad 250µA, 3MHz, 200V/µs Op Amps C-Load
Op Amps Stable Driving Any Capacitive Load
LTC1440 Micropower Comparator with 1% Reference 1.182V ±1% Reference, ±10mV (Max) Input Offset
LTC1443/LTC1444/LTC1445 Micropower Quad Comparators with 1% Reference LTC1443 Has 1.182V Reference, LTC1444/LTC1445 Have
1.221V Reference and Adjustable Hysteresis
LTC1474 Low Quiescent Current High Efficiency 10µA Standby Current, 92% Efficiency, Space Saving 8-Pin
Step-Down Converter MSOP Package
LT1495 1.5µA Max, Dual Precision Rail-to-Rail 375µV Max V
OS
, 250pA I
BIAS
, 25pA I
OS
Input and Output Op Amp
LT1521 300mA Low Dropout Regulator with Micropower 0.5V Dropout Voltage, 12µA Quiescent Current, Adjustable
Quiescent Current and Shutdown Output 3V, 3.3V and 5V Fixed
LT1634 Micropower Precision Shunt Voltage Reference 1.25V, 2.5V, 4.096V, 5V Outputs, 10µA Operating Current,
0.05% Initial Accuracy 25ppm/°C Max Drift, SO-8, MSOP and
TO-92 Packages
C-Load is a trademark of Linear Technology Corporation.
RELATED PARTS
The rectified output is monitored by the LTC1540 com-
parator. The internal reference is used to set up a threshold
of about 18mV at the inverting input. A rising edge at the
comparator output triggers a one shot that temporarily
enables answer back and any other pulsed functions.
The total supply current is 400nA. Among other monolithic
one shots, the CD4047 draws the least amount of transient
current.
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com