| Scale factor (V/decade) | 0.375 |
| Input current range (Min) (nA) | 0.1 |
| Input current range (Max) (mA) | 10 |
| Conformity error (initial 5 decades) (Max) (%) | 0.2 |
| Conformity error (initial 5 decades) (typ. over temp) (%/degree C) | 0.1 |
| Offset voltage (input amplifiers) (Max) (mV) | 4 |
| Vs (+/-) (Min) (V) | 4.8 |
| Vs (+/-) (Max) (V) | 11 |
| Iq (Max) (mA) | 15 |
| Dynamic range (Typ) (dB) | 160 |
| Reference type | Internal |
| Auxiliary op amps | 2 |
| Full-scale output voltage (Min) (+/- V) | -4.4 |
| Full-scale output voltage (Max) (+/- V) | 4.4 |
| Operating temperature range (C) | 0 to 70 |
| Specified voltage (+/- V) | 5 |
- ADVANTAGES:
- - Tiny for High Density Systems
- - Precision on One Supply
- - Fast Over Eight Decades
- - Fully-Tested Function
- TWO SCALING AMPLIFIERS
- WIDE INPUT DYNAMIC RANGE: Eight Decades, 100pA to 10mA
- 2.5V REFERENCE
- STABILE OVER TEMPERATURE
- LOW QUIESCENT CURRENT: 10mA
- DUAL OR SINGLE SUPPLY: ±5V, +5V
- PACKAGE: Small QFN-16 (4mm x 4mm)
- SPECIFIED TEMPERATURE RANGE: –5°C to +75°C
- APPLICATIONS
- ONET ERBIUM-DOPED FIBER OPTIC AMPLIFIER (EDFA)
- LASER OPTICAL DENSITY MEASUREMENT
- PHOTODIODE SIGNAL COMPRESSION AMP
- LOG, LOG-RATIO FUNCTION
- ANALOG SIGNAL COMPRESSION IN FRONT OF ANALOG-TO-DIGITAL (ADC) CONVERTER
- ABSORBANCE MEASUREMENT
The LOG114 is specifically designed for measuring low-level and wide dynamic range currents in communications, lasers, medical, and industrial systems. The device computes the logarithm or log-ratio of an input current or voltage relative to a reference current or voltage (logarithmic transimpedance amplifier).
High precision is ensured over a wide dynamic range of input signals on either bipolar (±5V) or single (+5V) supply. Special temperature drift compensation circuitry is included on-chip. In log-ratio applications, the signal current may be from a high impedance source such as a photodiode or resistor in series with a low impedance voltage source. The reference current is provided by a resistor in series with a precision internal voltage reference, photo diode, or active current source.
The output signal at VLOGOUT has a scale factor of 0.375V out per decade of input current, which limits the output so that it fits within a 5V or 10V range. The output can be scaled and offset with one of the available additional amplifiers, so it matches a wide variety of ADC input ranges. Stable dc performance allows accurate measurement of low-level signals over a wide temperature range. The LOG114 is specified over a -5°C to +75°C temperature range and can operate from -40°C to +85°C.
