LTC1540 Datasheet, PDF (12/12 Pages) Linear Technology – Nanopower Comparator with Reference

LTC1540
TYPICAL APPLICATION
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.
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.
λ /4
FB _10k
0.23λ
10nF
10nF
1N5712
2V TO 11V
12M
5
3₊
6
7
8
LTC1540
4_–
1
180k
2
CMOS Q
ONE SHOT
(CD4047) Q
1540 F10
Figure 10. Nanopower Field Detector
RELATED PARTS
PART NUMBER
LT ^® 1178/LT1179
LT1351
LT1352/LT1353
LTC1440
LTC1443/LTC1444/LTC1445
DESCRIPTION
Dual/Quad 17µA Precision Single Supply Op Amps
Single 250µA, 3MHz, 200V/µs Op Amp with Shutdown
Dual/Quad 250µA, 3MHz, 200V/µs Op Amps
Micropower Comparator with 1% Reference
Micropower Quad Comparators with 1% Reference
LTC1474
LT1495
LT1521
LT1634
Low Quiescent Current High Efficiency
Step-Down Converter
1.5µA Max, Dual Precision Rail-to-Rail
Input and Output Op Amp
300mA Low Dropout Regulator with Micropower
Quiescent Current and Shutdown
Micropower Precision Shunt Voltage Reference
C-Load is a trademark of Linear Technology Corporation.
COMMENTS
70µV Max V_OS, 5nA Max I_BIAS
C-Load^TM Op Amp Stable Driving Any Capacitive Load
C-Load Op Amps Stable Driving Any Capacitive Load
1.182V ±1% Reference, ±10mV (Max) Input Offset
LTC1443 Has 1.182V Reference, LTC1444/LTC1445 Have
1.221V Reference and Adjustable Hysteresis
10µA Standby Current, 92% Efficiency, Space Saving 8-Pin
MSOP Package
375µV Max V_OS, 250pA I_BIAS, 25pA I_OS
0.5V Dropout Voltage, 12µA Quiescent Current, Adjustable
Output 3V, 3.3V and 5V Fixed
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
12 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417^q [phone]
FAX: [phone]^q TELEX: 499-3977 ^q www.linear-tech.com
1540f LT/TP 0498 4K • PRINTED IN USA
© LINEAR TECHNOLOGY CORPORATION 1997