Overview
The LOG112AIDR, produced by Texas Instruments, is a precision logarithmic and log ratio amplifier. This integrated circuit is designed to compute the logarithm or log ratio of an input current relative to a reference current. It features a high degree of precision and a wide dynamic range, making it suitable for various applications requiring accurate logarithmic signal processing.
The device includes an on-chip 2.5V voltage reference, which can be used to generate a precision current reference using an external resistor. It is known for its low DC offset voltage and temperature drift, allowing accurate measurement of low-level signals over a specified temperature range of –5°C to +75°C.
Key Specifications
| Parameter | Condition | Min | Typ | Max | Units |
|---|---|---|---|---|---|
| Supply Voltage (V+ to V–) | ±4.5 | ±18 | V | ||
| Input Current Range | 100 pA | 3.5 mA | |||
| Output Voltage per Decade | 0.5 | V/decade | |||
| Log Conformity Error (5 decades) | 0.2% | % FSO | |||
| Log Conformity Error (7.5 decades) | 0.13% | % FSO | |||
| Temperature Range (Specified) | –5 | 75 | °C | ||
| Temperature Range (Operating) | –40 | 85 | °C | ||
| Quiescent Current (LOG112) | ±1.25 | ±1.75 | mA | ||
| Output Offset Voltage (Initial) | ±3 | ±15 | mV |
Key Features
- Easy-to-Use Complete Function: The LOG112AIDR provides a complete logarithmic and log ratio amplification function in a single package.
- On-Chip 2.5V Voltage Reference: This feature allows for the generation of a precision current reference using an external resistor.
- High Accuracy: The device offers high accuracy with a log conformity error of 0.2% over 5 decades and 0.13% over 7.5 decades.
- Wide Input Dynamic Range: The input current range spans from 100 pA to 3.5 mA, ensuring a wide dynamic range for various applications.
- Low DC Offset Voltage and Temperature Drift: This ensures accurate measurement of low-level signals over the specified temperature range.
- Output Scaling Amplifier: The output can be scaled using external resistors to adjust the gain according to application requirements.
Applications
- Data Compression: The logarithmic transfer function of the LOG112AIDR is useful in many applications requiring data compression, such as preceding an A/D converter to enhance dynamic range.
- Avalanche Photodiode Current Measurement: The device is suitable for measuring avalanche photodiode current due to its wide dynamic range.
- Single Supply Operation: The LOG112AIDR can be configured to operate with a single +5V supply, making it versatile for various system designs.
- Absorbance Measurement: It can be used in absorbance measurement setups due to its ability to handle low-level signals accurately.
- High-Speed Applications: The device's fast transient response and bandwidth make it suitable for high-speed applications such as in optical communication systems.
Q & A
- What is the primary function of the LOG112AIDR?
The primary function of the LOG112AIDR is to compute the logarithm or log ratio of an input current relative to a reference current.
- What is the output voltage per decade of input current for the LOG112AIDR?
The output voltage per decade of input current is 0.5V.
- What is the specified temperature range for the LOG112AIDR?
The specified temperature range is –5°C to +75°C.
- How does the LOG112AIDR handle voltage inputs?
Voltage inputs can be handled directly with series resistors, but the dynamic input range is limited to approximately three decades of input voltage due to voltage noise and offsets.
- What is the maximum input current rating for the LOG112AIDR?
The absolute maximum input current rating is 10mA to prevent excessive power dissipation.
- Can the LOG112AIDR operate on a single supply?
Yes, the LOG112AIDR can be configured to operate with a single +5V supply.
- What is the significance of the on-chip 2.5V voltage reference?
The on-chip 2.5V voltage reference allows for the generation of a precision current reference using an external resistor.
- How does the device's log conformity error affect its performance?
The log conformity error is a measure of the nonlinearity of the logarithmic transfer function and is expressed as a percent of the ideal full-scale output. It is a critical specification for ensuring the accuracy of the device.
- What are some common applications of the LOG112AIDR?
Common applications include data compression, avalanche photodiode current measurement, single supply operation, absorbance measurement, and high-speed applications.
- How does temperature affect the total error of the LOG112AIDR?
Temperature can affect the total error, which includes offset voltage, bias current, gain, and log conformity errors. The worst-case error for any given ratio of input currents is the largest of the two errors when the input currents are considered separately.
