説明

The LT1167 is a low power, precision instrumentation amplifier that requires only one external resistor to set gains of 1 to 10,000. The low voltage noise of 7.5nV/√Hz (at 1kHz) is not compromised by low power dissipation (0.9mA typical for ±2.3V to ±15V supplies).

The part’s high accuracy (10ppm maximum nonlinearity, 0.08% max gain error (G = 10)) is not degraded even for load resistors as low as 2k. The LT1167 is laser trimmed for very low input offset voltage (40μV max), drift (0.3μV/°C), high CMRR (90dB, G = 1) and PSRR (105dB, G = 1).

Low input bias currents of 350pA max are achieved with the use of superbeta processing. The output can handle capacitive loads up to 1000pF in any gain configuration while the inputs are ESD protected up to 13kV (human

body). The LT1167 with two external 5k resistors passes the IEC 1000-4-2 level 4 specification.

The LT1167, offered in 8-pin PDIP and SO packages, requires significantly less PC board area than discrete multiop amp and resistor designs.

The LT1167-1 offers the same performance as the LT1167, but its input current characteristic at high common mode voltage better supports applications with high input impedance (see the Applications Information section).

 

特徴

Single Gain Set Resistor: G = 1 to 10,000

Gain Error: G = 10, 0.08% Max

Input Offset Voltage Drift: 0.3μV/°C Max

Meets IEC 1000-4-2 Level 4 ESD Tests with

Two External 5k Resistors

Gain Nonlinearity: G = 10, 10ppm Max

Input Offset Voltage: G = 10, 60μV Max

Input Bias Current: 350pA Max

PSRR at G = 1: 105dB Min

CMRR at G = 1: 90dB Min

Supply Current: 1.3mA Max

Wide Supply Range: ±2.3V to ±18V

1kHz Voltage Noise: 7.5nV/√Hz

0.1Hz to 10Hz Noise: 0.28μVP-P

Available in 8-Pin PDIP and SO Packages

 

 アプリケーション

Bridge Amplifiers

Strain Gauge Amplifi ers

Thermocouple Amplifi ers

Differential to Single-Ended Converters

Medical Instrumentation

アプリケーション情報

The amplitude and frequency of the interference can have an adverse effect on an instrumentation amplifier’s input stage by causing an unwanted DC shift in the amplifier’s input offset voltage. This well known effect is called RFI rectification and is produced when out-of-band interference is coupled (inductively, capacitively or via radiation) and rectified by the instrumentation amplifier’s input transistors. These transistors act as high frequency signal detectors, in the same way diodes were used as RF envelope detectors in early radio designs. Regardless of the type of interference or the method by which it is coupled into the circuit, an out-of-band error signal appears in series with the instrumentation amplifier’s inputs.

To significantly reduce the effect of these out-of-band signals on the input offset voltage of instrumentation amplifiers, simple lowpass filters can be used at the inputs. These filters should be located very close to the input pins of the circuit. An effective filter configuration is illustrated in Figure 5, where three capacitors have been added to the

inputs of the LT1167. Capacitors CXCM1 and CXCM2 form lowpass filters with the external series resistors RS1, 2 to any out-of-band signal appearing on each of the input traces. Capacitor CXD forms a filter to reduce any unwanted signal that would appear across the input traces. An added

benefit to using CXD is that the circuit’s AC common mode rejection is not degraded due to common mode capacitive imbalance.

Setting the time constants requires a knowledge of the frequency, or frequencies of the interference. Once this frequency is known, the common mode time constants can be set followed by the differential mode time constant. To avoid any possibility of inadvertently affecting the signal

to be processed, set the common mode time constant an order of magnitude (or more) larger than the differential mode time constant. Set the common mode time constants such that they do not degrade the LT1167’s inherent AC CMR. Then the differential mode time constant can be set for the bandwidth required for the application. Setting the differential mode time constant close to the sensor’s BW also minimizes any noise pickup along the leads. To avoid any possibility of common mode to differential mode signal conversion, match the common mode time constants to 1% or better. If the sensor is an RTD or a resistive strain gauge, then the series resistors RS1, 2 can be omitted, if the sensor is in proximity to the instrumentation amplifier.