AD620
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| 7 | 20kV |
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3kV | 3kV |
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8 |
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| G=100 | AD620B | 6 | IN | DIGITAL | |
3kV | 3kV | 499V | 5 | 10kV | ADC | ||
DATA | |||||||
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| AD705 | AGND |
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| 20kV |
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1.7mA |
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| 1.3mA | 0.6mA |
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| 0.10mA |
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| MAX | MAX |
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Figure 35. A Pressure Monitor Circuit which Operates on a +5 V Single Supply
Pressure Measurement
Although useful in many bridge applications such as weigh scales, the AD620 is especially suitable for higher resistance pressure sensors powered at lower voltages where small size and low power become more significant.
Figure 35 shows a 3 kΩ pressure transducer bridge powered from +5 V. In such a circuit, the bridge consumes only 1.7 mA. Adding the AD620 and a buffered voltage divider allows the signal to be conditioned for only 3.8 mA of total supply current.
Small size and low cost make the AD620 especially attractive for voltage output pressure transducers. Since it delivers low noise and drift, it will also serve applications such as diagnostic non- invasive blood pressure measurement.
Medical ECG
The low current noise of the AD620 allows its use in ECG monitors (Figure 36) where high source resistances of 1 MΩ or higher are not uncommon. The AD620’s low power, low supply voltage requirements, and
Furthermore, the low bias currents and low current noise coupled with the low voltage noise of the AD620 improve the dynamic range for better performance.
The value of capacitor C1 is chosen to maintain stability of the right leg drive loop. Proper safeguards, such as isolation, must be added to this circuit to protect the patient from possible harm.
PATIENT/CIRCUIT |
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PROTECTION/ISOLATION |
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| R1 | R3 |
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| 0.03Hz |
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C1 | 10kV | 24.9kV | RG |
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AD620A | HIGH | G = 143 | OUTPUT | |||||
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| R2 | 8.25kV |
| PASS |
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| G = 7 | FILTER |
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| 1MV | 24.9kV |
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AD705J |
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Figure 36. A Medical ECG Monitor Circuit
REV. E |
