High Speed, 200 dB Range,
Logarithmic
Data Sheet
A single positive supply of 5 V is all that is required for operation
over a specified 1 pA to 3 mA input range. Dual-supply operation
extcified input current range to 10 mA.
FEATURES
Optimized for very fast response at all input currents
Overall bandwidth of >4 MHz for inputs >1 µA
Bandwidth: 25 kHz at input of 1 nA and 350 kHz at 10 nA
10 decades of input range: 1 pA to 10 mA
Law conformance: ±0.25 dB from 100 pA to 100 µA
Log ratio or fixed-intercept operation
Precision voltage references and reference current
Adaptive photodiode (PD) bias for low dark current
Programmable log slope and intercept
Default log slope of 10 mV/dB at VLOG pin
Single- or dual-supply operation
Thccepts two current inputs to the logarithmic
argument. The numerator input, INUM, flows in the collector of an
NPN transistor, connected in a feedback path around a low offset
JFET amplifier. The denominator current, IDEN, is treated in the
same way, which allows for log ratio operation. The input summing
nodes (INUM and IDEN) operate at a constant default voltage of
1.5 V. The VSM1 to VSM4 pins flank the INUM and IDEN inputs
to provide a guard voltage to minimize leakage currents.
Adaptive photodiode biasing is provided for optical measurements.
A monitor current 1.1 times INUM is output at the IMON pin, and
an external resistor, RMNTR, at 10 times the photodiode series
resistance (RS) applies a voltage across the photodiode that
1st order keeps the internal PD junction at 0 V to minimize
dark current.
APPLICATIONS
High accuracy optical power measurement
Wide range baseband log compression
Versatile detector for high speed APC loops
GESCRIPTION
The VLOG output is buffered and can be rescaled through
internal gain setting resistors. The internal ILOG varies from
−400 µA to +400 µA as INUM changes over 10 decades from 1 pA
to 10 mA. This corresponds to 0.5 V the VLOG pin
in the default configuration shown i
Ths a high speed logarithmic converter with fast
response and loa 200 dB (1 pA to 10 mA) measure-
ment range. Trovides a nominal logarithmic slope of
10 mV/dB (200 mV/decade); other values are easily configured.
Logarithmic intercept can be programmed over a wide range
with the internal 100 nA current source or externally for log ratio
applications. The default intercept value of 3.162 fA places the
midpoint of the measurement range of 100 nA at VLOG = 1.5 V.
Accurate 1.5 V (Pin 1P5V) and 2.0 V (Pin 2VLT) reference outputs
alloositioning of the intercept using external resistors.
Ths available in a 32-lead, 5 mm × 5 mm LFCSP
and specified for operation from −40°C to +85°C.
SIMPLIFIED BLOCK DIAGRAM
BSDC 2VLT VPOS
IMON
VNUM
INNM 1P5V
31
DCBI
30
32
26
28
17
29
27
INPS
24
1.5V
2V
MONITOR AND
PD BIAS
R
INMS
BIAS AND
MNTR
100nA
VSM1
VSM2
23
22
(1.1× I
)
V
2
NUM
REF
VLOG
1.5V
3
ADL5304
INUM
SCL1
SCL2
4
5
6
7
8
V
V
I
21
NUM
LOG
5kΩ
7.5kΩ
5kΩ
IDEN
TEMPERATURE
COMPENSATION
20
19
IREF
VSM3
SCL3
DEN
ACOM
18
VSM4
1.5V
COMM NMFS VNEG DNFS ACOM HFCP
9
10 11
12
13
14
15
16
VDEN
INDN
1kΩ
1kΩ
V
NEG
Figure 1.
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
©2011–2016 Analog Devices, Inc.
全部评论(0)