Precision Sensor Signal Conditioning Solution

This signal conditioning solution is optimized for bridge-type sensors including strain gauges, load cells, and pressure sensors. The differential input configuration and high CMRR effectively reject common-mode noise from long sensor cables. The ultra-low offset voltage is ideal for mV-level sensor outputs requiring high gain. Thermocouples benefit from the low offset drift for accurate cold junction compensation. RTD sensors work well with the constant current excitation and ratiometric measurement capability. The solution can be adapted for piezoelectric sensors with modified filtering for AC coupling. Capacitive sensors requiring charge amplification can use modified configurations. The wide gain range accommodates sensors with outputs from microvolts to volts. Contact LiTong FAEs for specific sensor interface recommendations.

For bridge sensors, use the standard configuration. For thermocouples, add cold junction compensation. Contact FAE for other sensor types.

Total error budget calculation must include all error sources: amplifier offset voltage (50μV), offset drift (0.5μV/°C × temperature range), gain error from resistors (0.1% resistors = 0.2% worst-case gain error), reference accuracy (0.5%), reference drift (20ppm/°C), CMRR error (input CM voltage / CMRR), and PSRR error (supply variation / PSRR). Combine systematic errors (offset, gain) algebraically and random errors (noise) in RSS (root-sum-square). For a typical strain gauge application with gain of 100: offset contributes 5mV, drift (50°C range) contributes 2.5mV, gain error contributes 0.2%, reference contributes 0.5%. Total systematic error is approximately 0.7% + 7.5mV. Design with margin - target 70% of allowable error budget to account for component variations and aging.

Use our Error Budget Calculator spreadsheet for comprehensive analysis. Leave 30% margin in your error budget for component variations.

PCB layout is critical for achieving datasheet DC accuracy. Place decoupling capacitors (0.1μF ceramic) within 2mm of amplifier supply pins with short, wide traces. Implement guard rings around high-impedance input traces - connect guard ring to input common-mode voltage to intercept leakage currents. Use Kelvin connections for sense resistors to eliminate trace resistance errors. Maintain symmetrical layout for differential inputs to preserve CMRR. Route input traces away from digital switching signals to prevent capacitive coupling. Use a solid ground plane for low impedance returns. For thermocouple applications, minimize junctions and use isothermal blocks for cold junction compensation. Thermal gradients across the PCB can create thermocouple effects - keep heat sources away from precision circuitry. Verify layout with FAE review before production.

Follow the PCB Layout Guidelines document. Submit your layout for FAE review to ensure optimal performance.

Yes, this solution can be extended for multi-channel systems using multiplexing. Use GS4157 analog switches to select between multiple sensors sharing a single amplifier chain. For multiplexed systems, verify settling time requirements - the amplifier must settle to required accuracy before ADC conversion. Settling time depends on amplifier bandwidth, slew rate, and any RC filtering. For 12-bit accuracy, allow 8-10 time constants

for 16-bit, allow 11-12 time constants. Calculate maximum channel switching rate based on settling requirements. Alternatively, use multiple amplifier channels (GS8552 dual, GS8554 quad) for simultaneous sampling of all channels. This eliminates settling time constraints but increases power consumption and cost. For high-channel-count systems, consider a hybrid approach with multiple multiplexed amplifier chains.

For low-channel-count systems, use per-channel amplifiers. For high-channel-count, implement multiplexing with adequate settling time.

For battery-powered applications, minimize power through several strategies. Use GS8551 instead of GS8511 for slightly lower current (45μA vs 40μA is negligible, but GS8551 may offer better bandwidth/power trade-off). Implement duty-cycled operation - power down the amplifier between measurements using the shutdown feature if available, or use a load switch. Minimize measurement frequency to the minimum required by the application. Use higher value resistors in the feedback network (but calculate noise impact). Consider using GS432 1.25V reference instead of GS431 for lower voltage operation. For intermittent measurements, the average current can be very low even with higher peak current. Calculate total energy consumption based on duty cycle. Use the lowest supply voltage that meets your headroom requirements.

Implement duty-cycled operation for lowest average power. Calculate energy consumption based on your specific duty cycle and measurement frequency.

Filtering requirements depend on sensor type and application. For DC measurements like strain gauges, implement simple RC low-pass filters with cutoff at 10-100Hz to remove 50/60Hz power line interference. Use 100nF film capacitors for low dielectric absorption. For dynamic measurements like vibration sensors, use higher cutoff frequencies (1-10kHz) and consider anti-aliasing before ADC. For thermocouples, very low cutoff (1-5Hz) removes thermal noise while preserving slow temperature changes. For pressure sensors with pulsatile signals (blood pressure), use 100-200Hz cutoff. Active filtering using GS8551 can provide steeper roll-off than passive RC. Second-order Sallen-Key filters provide 40dB/decade attenuation. Always verify filter settling time impact on system response. Include EMI filtering at the input connectors for industrial applications.

Match filter cutoff to your signal bandwidth. Use active filters for steeper roll-off when required. Verify settling time impact.