Measure resistances easily, without reference resistor or current source

25 October 2000 Analogue, Mixed Signal, LSI

The circuit of Figure 1 shows how to use the new LT1168 instrumentation amplifier to achieve a precision resistance-to-voltage conversion as simply as possible. Normally, the resistor across pins 1 and 8 is the gain-set resistor and the voltage across pins 3 and 2 is the variable to be measured. In this case, however, the 1,25 V reference establishes a fixed input voltage so that the variable to be measured is now the resistance. The equation for VOUT vs RT is VOUT = 1,25 V . 49,4 kOhm/RT.

Given the limitation on output swing (with the supply voltages shown), the smallest measurable resistance is about 4,5K. The highest resolvable resistance is limited to about 200M by the 300 µV output offset voltage of the LT1168.

The 0,05% accuracy of the LT1634 is not an issue here because it is subtracted at the Ref pin of the LT1168 and only contributes to gain error.

Figure 2 shows output voltage vs temperature for 10 and 100K (at 25°C) thermistors from two manufacturers. Thermistors are difficult to linearise, so although the output is still not linear with temperature, it can, at least, be read directly by an ADC and compared against a lookup table. The circuit has good noise immunity but does not tolerate capacitance at pin 1 or 8 and so is not ideal for resistive devices placed remotely from the LT1168.

Further reading:

IMU with dual-sensing capability
EBV Electrolink Analogue, Mixed Signal, LSI
ST’s 6-axis inertial measurement unit integrates a dual accelerometer up to 320g and embedded AI for activity tracking and high-impact sensing.

Read more...

---

Plural data converter series
Analogue, Mixed Signal, LSI
Silanna Semiconductor has announced the launch of Plural, a new generation of data converters for customers eager to find a more available, affordable, high-performance alternative to existing brands.

Read more...

---

Precision JFET op-amp
Altron Arrow Analogue, Mixed Signal, LSI
The specifications of the ADA4620 make it optimal as a front-end amplifier in a data-acquisition system, or for a TIA circuit with high input impedance.

Read more...

---

A new era in modular I/O solutions
Rugged Interconnect Technologies Analogue, Mixed Signal, LSI
Aerospace and defence system designers are demanding scalable and high-performance I/O solutions and while traditional mezzanine standards have proven reliable, they often fall short of meeting modern bandwidth, size, and flexibility requirements.

Read more...

---

High voltage instrument op-amp
iCorp Technologies Analogue, Mixed Signal, LSI
The SGM621B is a high accuracy, high voltage instrumentation amplifier, which is designed to set any gain from 1 to 10 000 with one external resistor.

Read more...

---

High-speed SAR ADC simplifies design
Altron Arrow Analogue, Mixed Signal, LSI
The ADI AD4080 simplifies data converter integration by integrating a low drift reference buffer, low dropout regulators and a 16K result data FIFO buffer.

Read more...

---

2-wire quad voltage output DAC
Altron Arrow Analogue, Mixed Signal, LSI
The DAC has a 2-wire serial interface that operates at clock rates up to 400 kHz, and this interface is SMBus compatible, allowing multiple devices to be placed on the same bus.

Read more...

---

Dual-channel ADC for RF applications
RFiber Solutions Analogue, Mixed Signal, LSI
The ARF0471 from Advanced RF is a dual-channel, 14-bit, 3 GSPS ADC, which features an on-chip buffer and sample-and-hold circuit.

Read more...

---

Infineon launches Edge Ai software solution
Altron Arrow Analogue, Mixed Signal, LSI
Infineon has introduced DEEPCRAFT, a new software solution category brand for Edge AI and machine learning, after the company recognised the huge potential of Edge AI for the market.

Read more...

---

16-bit voltage output denseDAC
Altron Arrow Analogue, Mixed Signal, LSI
The AD5766 uses a versatile four-wire serial interface that operates at clock rates of up to 50 MHz for write mode, and is compatible with SPI, QSPI, MICROWIRE, and DSP interface standards.

Read more...

---