How it works
The designed instrumentation amplifier extracts very low differencial mode signal from very noisy common mode signals by means of a three opamp array. The differential gain can be changed by two digital bits called "Sel_26dB" and "Sel_42dB", when Sel_26dB = 0 Sel_42dB = 0 the differential gain is 0 dB, when Sel_26dB = 1 and Sel_42dB = 0 the differential gain is 26 dB, when Sel_26dB = 1 and Sel_42dB = 1 the differential gain is 46 dB. In all cases the CMRR is 120 dB. The designed instrumentation amplifier also included a sense circuits that helps to stabilize the analog ground.
How to test
- Apply a DC level equals to vdd = 1.8V and vss = 0V.
- Set the following bits to Sel_26dB = 0 and Sel_42dB = 0.
- Apply a 1 mV differential signal into Vip and Vin analog ports using a balum.
- Measure the differential responds at node Vo using Keysight-E5061B ENA vector network analyzer, a 0 dB gain shall be expected.
- Apply a 1 mV common signal into Vip and Vin analog ports.
- Measure the common responds at node Vo using Keysight-E5061B ENA vector network analyzer.
- Performs the substraction of the differential gain and the common gain, the CMRR responds should be obtined.
- Set the following bits to Sel_26dB = 1 and Sel_42dB = 0.
- Apply a 1 mV differential signal into Vip and Vin analog ports using a balum.
- Measure the differential responds at node Vo using Keysight-E5061B ENA vector network analyzer, a 26 dB gain shall be expected.
- Apply a 1 mV common signal into Vip and Vin analog ports.
- Measure the common responds at node Vo using Keysight-E5061B ENA vector network analyzer.
- Performs the substraction of the differential gain and the common gain, the CMRR responds should be obtined.
- Set the following bits to Sel_26dB = 1 and Sel_42dB = 1.
- Apply a 1 mV differential signal into Vip and Vin analog ports using a balum.
- Measure the differential responds at node Vo using Keysight-E5061B ENA vector network analyzer, a 42 dB gain shall be expected.
- Apply a 1 mV common signal into Vip and Vin analog ports.
- Measure the common responds at node Vo using Keysight-E5061B ENA vector network analyzer.
- Performs the substraction of the differential gain and the common gain, the CMRR responds should be obtined.
External hardware
- 1 PCB
- 1 Balum
- 1 Keysight-E5061B ENA vector network analyzer
- 3 Female-Female BNC cable.
- 1 Female-Female-Female BNC T-adapter
- 1 Keithly 2231A power supply
- 1 Agilent 34401A digital multimeter