SBOT049 April   2024 BUF802 , OPA814 , OPA817 , OPA859

 

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Wide-bandwidth data-acquisition (DAQ) systems (for example, oscilloscopes and active probes) use an analog front end (AFE) signal chain to capture high-frequency signals and fast-transient pulses. The input amplifier is the first stage in the signal chain of a wide-bandwidth DAQ system. The high input impedance (high-Z) and low bias current inputs of a JFET-input amplifier allow the measurement of small signals and help set the noise floor of the entire signal chain. JFET amplifiers are used as either unity-gain buffers (Figure 1) or in noninverting gain configurations (Figure 2) between the analog input signal and the analog-to-digital converter (ADC).

GUID-20240201-SS0I-1BSH-BWRT-PL5BVZST4SX2-low.svg Figure 1 Input JFET Amplifier in a Buffer Configuration in a Generic DAQ Front End
GUID-20240201-SS0I-ML8T-2BRP-MC52J57D5G5J-low.svg Figure 2 Input JFET Amplifier in a Gain Configuration in a Generic DAQ Front End

Design Considerations

  • Large signal bandwidth to measure a wide-frequency range of signals
  • High-input impedance to prevent the loading of the measured signals
  • Low noise to detect low-magnitude signals
  • DC accuracy and precision for precise measurements
  • Low bias current to minimize offset
  • Output voltage swing to provide compatibility with subsequent stages
  • Power consumption for battery-operated or thermal-sensitive systems
  • Gain configuration or unity gain
  • Learn about amplifier parameters with TI precision lab video
  • Ask a question on our TI E2E™ forums
  • Table 1 and Table 2 list the device selections
Table 1 Recommended < 12V Parts
Parameter BUF802 OPA818 OPA859 OPA817 OPA814
VS MIN to MAX (V) 9 to 13 6 to 13 3.3 to 5.25 6 to 12.6 6 to 12.6
Large Signal Bandwidth (2VPP) (MHz) 1600 400 400 250 200
Slew rate (V/μs) 7000 1400 1150 100 700
Input impedance (GΩ) 50 500 1 60 60
Noise (nV/√Hz) 2.3 2.2 3.3 4.5 5.3
Maximum Drift (μV/°C) 1330(1) 20 N/A 3.5 3.5
Fixed Gain (V/V) Yes No No No No
Maximum Bias Current (pA) 25 25 5 20 20
Output Voltage Swing (V) VS+ – 1.9,
VS– + 3.4		 VS+ – 0.5,
VS– + 0.5		 VS+ – 0.9,
VS– + 2.2		 ±3.9 ±3.9
IQ (TYP) (mA) 34 27.7 20.5 23.5 16
Smallest Package Size (mm) VQFN
3 × 3		 WSON
3 × 3		 WSON
3 × 3		 WSON
3 × 3		 SOT-23
2.9 × 2.8
(1) BUF802 package size and drift represent values for the standalone device not in a composite configuration.
Table 2 Recommended > 24V Parts
Parameter THS4631 OPA810
VS Min to Max (V) 10 to 32 4.75 to 24
Large Signal BW (2VPP) (MHz) 230 70
Slew rate (V/μs) 1000 200
Input impedance (GΩ) 10 12
Noise (nV/√Hz) 7 6.3
Maximum Drift (μV/℃) 10 10
Fixed Gain (V/V) No No
Max Bias Current (pA) 100 20
Output Voltage Swing (V) ±13.5 VS+ – 0.11,
VS– + 0.08
IQ (typ) (mA) 11.5 3.7
Smallest Package Size (mm) HVSSOP
3 × 4.9		 SC70
2 × 1.25

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