Offset Gain Module
Functional Description
Brief Description: This module produces an output equal to the sum of two scaled input signals. There are two outputs provided on parallel channels.
The schematic of a typical Summing Amplifier is presented below. To enlarge the schematic, click on it.
The summing amplifier scales and adds two input signals. The input current is Iin = V1/R1 + V2/R2 + V3/R3. This gives an output voltage of Vout = -(V1 + V2 + V3). The schematic shows all of the resistor values to be equal, however, this need not be the case. If the resistors are unequal the output sum is a weighted sum of the inputs. Also, the inputs can be either positive or negative.
Front Panel
Front Panel of Offset Gain
Module
Inputs:
Two separate inputs (V1 and V2) are applied by the BNC connectors on the front panel.
Outputs:
Two parallel output channels are provided on the parallel outputs.
Input Selection:
The input to each amplifier may be selected by using the three-way input selection switch with three options:
- Normal: input is connected to the front panel
- Ground: input is grounded to disconnect the input signal
- 1 Volt: input is connected to a 1 Volt Reference Channel
Rotary Gain Switch
Varies the gain multiplier from 1000 to 0.001 in steps of 10.
The Gain Trim Potentiometer
Adjusts the amplifier gain value by a scale factor ranging from +1 to -1.
Gain Selection
The gain of each amplifier is determined by the product of the rotary gain switch and trim gain.
Circuit Diagram
Offset Gain Module Schematic
The figure above shows the schematic of the Offset Gain Module used in this lab.
Note: The frequency response of the module decreases for higher gains.
Operation
Gain Setting
To set the gain of an amplifier, connect its input switch to +1Volt and the input of the other amplifier to GROUND. Adjust the gain-trim to get the desired output values.
List of Components
· 1 LT1001 Operational Amplifier
· 5 LT1001 Operational Amplifier
· Dielectric Capacitors
· +/- 10% Resistors
· 2 Potentiometers
Functional Specifications
This module requires +/- 15 Volt power supply to operate. The following list shows the output gains of each summing amplifier. The list shows the resistances and the corresponding gains.
|
Gain |
Resistance (Ohms) |
|
1000 |
1M |
|
100 |
100K |
|
10 |
10K |
|
1 |
1K |
|
0.1 |
100 |
|
0.01 |
10 |
