Datasheet LT1920 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | Single Resistor Gain Programmable, Precision Instrumentation Amplifier |
| Pages / Page | 12 / 10 — THEORY OF OPERATIO. Figure 3. Providing an Input Common Mode Current … |
| File Format / Size | PDF / 308 Kb |
| Document Language | English |
THEORY OF OPERATIO. Figure 3. Providing an Input Common Mode Current Path. APPLICATIONS INFORMATION. Input Protection
Model Line for this Datasheet
Text Version of Document
LT1920
U THEORY OF OPERATIO
– – – MICROPHONE, THERMOCOUPLE RG LT1920 HYDROPHONE, RG LT1920 RG LT1920 ETC + + + 10k 200k 200k CENTER-TAP PROVIDES BIAS CURRENT RETURN 1920 F03
Figure 3. Providing an Input Common Mode Current Path U U W U APPLICATIONS INFORMATION
The LT1920 is a low power precision instrumentation V V CC CC OPTIONAL FOR HIGHEST amplifier that requires only one external resistor to accu- J1 J2 ESD PROTECTION 2N4393 2N4393 rately set the gain anywhere from 1 to 1000. The output VCC R can handle capacitive loads up to 1000pF in any gain IN + configuration and the inputs are protected against ESD strikes up to 13kV (human body). OUT RG LT1920 REF
Input Protection
RIN – The LT1920 can safely handle up to ±20mA of input VEE 1920 F04 current in an overload condition. Adding an external 5k
Figure 4. Input Protection
input resistor in series with each input allows DC input fault voltages up to ±100V and improves the ESD immu- nity to 8kV (contact) and 15kV (air discharge), which is the sors may be connected to signal conditioning circuitry, IEC 1000-4-2 level 4 specification. If lower value input using shielded or unshielded twisted-pair cabling, the ca- resistors are needed, a clamp diode from the positive bling may act as antennae, conveying very high frequency supply to each input will maintain the IEC 1000-4-2 interference directly into the input stage of the LT1920. specification to level 4 for both air and contact discharge. The amplitude and frequency of the interference can have A 2N4393 drain/source to gate is a good low leakage diode an adverse effect on an instrumentation amplifier’s input for use with 1k resistors, see Figure 4. The input resistors stage by causing an unwanted DC shift in the amplifier’s should be carbon and not metal film or carbon film. input offset voltage. This well known effect is called RFI rectification and is produced when out-of-band interfer-
RFI Reduction
ence is coupled (inductively, capacitively or via radiation) In many industrial and data acquisition applications, and rectified by the instrumentation amplifier’s input tran- instrumentation amplifiers are used to accurately amplify sistors. These transistors act as high frequency signal small signals in the presence of large common mode detectors, in the same way diodes were used as RF voltages or high levels of noise. Typically, the sources of envelope detectors in early radio designs. Regardless of these very small signals (on the order of microvolts or the type of interference or the method by which it is millivolts) are sensors that can be a significant distance coupled into the circuit, an out-of-band error signal ap- from the signal conditioning circuit. Although these sen- pears in series with the instrumentation amplifier’s inputs. 10
U THEORY OF OPERATIO
– – – MICROPHONE, THERMOCOUPLE RG LT1920 HYDROPHONE, RG LT1920 RG LT1920 ETC + + + 10k 200k 200k CENTER-TAP PROVIDES BIAS CURRENT RETURN 1920 F03
Figure 3. Providing an Input Common Mode Current Path U U W U APPLICATIONS INFORMATION
The LT1920 is a low power precision instrumentation V V CC CC OPTIONAL FOR HIGHEST amplifier that requires only one external resistor to accu- J1 J2 ESD PROTECTION 2N4393 2N4393 rately set the gain anywhere from 1 to 1000. The output VCC R can handle capacitive loads up to 1000pF in any gain IN + configuration and the inputs are protected against ESD strikes up to 13kV (human body). OUT RG LT1920 REF
Input Protection
RIN – The LT1920 can safely handle up to ±20mA of input VEE 1920 F04 current in an overload condition. Adding an external 5k
Figure 4. Input Protection
input resistor in series with each input allows DC input fault voltages up to ±100V and improves the ESD immu- nity to 8kV (contact) and 15kV (air discharge), which is the sors may be connected to signal conditioning circuitry, IEC 1000-4-2 level 4 specification. If lower value input using shielded or unshielded twisted-pair cabling, the ca- resistors are needed, a clamp diode from the positive bling may act as antennae, conveying very high frequency supply to each input will maintain the IEC 1000-4-2 interference directly into the input stage of the LT1920. specification to level 4 for both air and contact discharge. The amplitude and frequency of the interference can have A 2N4393 drain/source to gate is a good low leakage diode an adverse effect on an instrumentation amplifier’s input for use with 1k resistors, see Figure 4. The input resistors stage by causing an unwanted DC shift in the amplifier’s should be carbon and not metal film or carbon film. input offset voltage. This well known effect is called RFI rectification and is produced when out-of-band interfer-
RFI Reduction
ence is coupled (inductively, capacitively or via radiation) In many industrial and data acquisition applications, and rectified by the instrumentation amplifier’s input tran- instrumentation amplifiers are used to accurately amplify sistors. These transistors act as high frequency signal small signals in the presence of large common mode detectors, in the same way diodes were used as RF voltages or high levels of noise. Typically, the sources of envelope detectors in early radio designs. Regardless of these very small signals (on the order of microvolts or the type of interference or the method by which it is millivolts) are sensors that can be a significant distance coupled into the circuit, an out-of-band error signal ap- from the signal conditioning circuit. Although these sen- pears in series with the instrumentation amplifier’s inputs. 10
