SGM834B
140dB Range (1nA to 10mA)
Logarithmic Current-to-Voltage Converter
GENERAL DESCRIPTION
FEATURES
The SGM834B is a single-supply logarithmic current-to-
voltage converter for measuring the low frequency
current signals over a large range from 1nA to 10mA.
With capabilities such as photodiode adaptive biasing,
active-shielding (guard driving), output buffer amplifier
conditioning and voltage reference on a single chip, this
device is optimized for measuring the power of optical
signals by using a photodiode operating in the photo
current mode. The measured current is converted and
compressed to a logarithmic voltage by using transistor
I-V characteristics and a compensation circuit.
● Patents Pending Proprietary Circuits
● Seven Full Decades Range
● 3V to 5.5V Single-Supply Operation
● Low Power and Temperature Stable
● Precise Trimmed Scaling
● 10mV/dB Logarithmic Slope at VLOG Pin
● 100pA Basic Logarithmic Intercept
● Simple Slope and Intercept Adjustments
● 15V/μs Slew Rate
● 3.3mA (TYP) Quiescent Current (Enabled)
● 9μA (TYP) Shutdown Current (Disabled)
● Available in a Green TSSOP-14 Package
The SGM834B operates with a single 3V to 5.5V supply
and is equipped with a disable input to shut down the
device. The input current (IPD) is converted to an
internal 40µA/dec logarithmic scaled current that is
injected into an internal 5kΩ resistance to provide an
output voltage with 10mV/dB (or 200mV/dec)
logarithmic slope on the VLOG output pin. This slope
can be reduced by an external shunt resistor. The
intercept point (the output voltage corresponding to the
selected intercept current) and the scale (to change the
slope) can be adjusted by the on-chip buffer amplifier.
APPLICATIONS
High Accuracy Optical Power Measurement
Wide Range Baseband Log Data Compression
Versatile Detector for Automatic Power Control Loops
This device is available in a Green TSSOP-14 package
and is specified over a temperature range of -40℃ to
+85℃.
TYPICAL APPLICATION
VOUT
500mV/dec
VP
10
12
VPS
11
VOUT
RA
15kΩ
RB
VPS
10kΩ
IPD
3
4
5
6
13
8
VSUM
BFNG
VLOG
BFIN
CFLT
INPT
200mV/dec
9
SGM834B
VSUM
VPDB
10nF
10nF
7
VREF
GND
AGND
14
PWDN
2
0.1μF
1
Figure 1. Typical Application Circuit
SG Micro Corp
MARCH2022–REV. A
www.sg-micro.com