Hi,
I'm trying to amplify very small signals in the range of 200uV max. This is something normal using dual-voltage circuit, but I'm trying to build the device with a single uni-polar battery.
I'm using a biasing voltage by dividing the battery voltage into two. After this, an OPA2350 is used as an input buffer. The buffered input is then connected to inputs of AD623. The full schematics is shown below.
Here, you can see that R5 and R6 provide the voltage division, R11 feeds the voltage to the input, and R10 represents the device input resistance. These resistors are all calculated to provide the highest input amplitude. Following this stage are two OPA2350s to buffer positive and negative inputs. The buffered inputs are then connected to AD623 (in the picture it is AD620). Also, the Gain resistor is 1.02K 1% resistor as suggested by the datasheet. R4 and R7 provide an alternative current circuit. Finally, U2 provides the virtual ground, and U6 is integrator feedback to compensate input offsets.
I can't perform tests with actual subjects, but in my lab I have a signal generator that provides sinusoidal wave with a minimum amplitude of 7mV peak. This worked for me before by replacing it with VG1 as the input source.
Now, as I expect, I should get a fixed gain of 100, or a gain of around 50 because of the voltage dividers. However, I can't get any gains more than 2. It doesn't matter if I set the gain resistor for 1000, 100, or even 10. I don't get the amplification I want. What do you think the problem is?
I'm trying to amplify very small signals in the range of 200uV max. This is something normal using dual-voltage circuit, but I'm trying to build the device with a single uni-polar battery.
I'm using a biasing voltage by dividing the battery voltage into two. After this, an OPA2350 is used as an input buffer. The buffered input is then connected to inputs of AD623. The full schematics is shown below.
Here, you can see that R5 and R6 provide the voltage division, R11 feeds the voltage to the input, and R10 represents the device input resistance. These resistors are all calculated to provide the highest input amplitude. Following this stage are two OPA2350s to buffer positive and negative inputs. The buffered inputs are then connected to AD623 (in the picture it is AD620). Also, the Gain resistor is 1.02K 1% resistor as suggested by the datasheet. R4 and R7 provide an alternative current circuit. Finally, U2 provides the virtual ground, and U6 is integrator feedback to compensate input offsets.
I can't perform tests with actual subjects, but in my lab I have a signal generator that provides sinusoidal wave with a minimum amplitude of 7mV peak. This worked for me before by replacing it with VG1 as the input source.
Now, as I expect, I should get a fixed gain of 100, or a gain of around 50 because of the voltage dividers. However, I can't get any gains more than 2. It doesn't matter if I set the gain resistor for 1000, 100, or even 10. I don't get the amplification I want. What do you think the problem is?