How to convert a dual power supply circuit to a single power supply circuit
1.1 Power supply and single power supply
All operational amplifiers have two power pins, usually labeled as VCC+and VCC - in the documentation, but sometimes their labels are VCC+and GND. This is because some authors of data manuals attempt to differentiate this labeling difference between single power operational amplifiers and dual power operational amplifiers. However, this does not mean they must use it that way - they may be able to work at other voltages. When the operational amplifier is not powered by the default voltage, it is necessary to refer to the operational amplifier's data manual, especially the absolute maximum supply voltage and voltage swing instructions.
The vast majority of analog circuit designers know how to use operational amplifiers under dual power supply voltage conditions, such as the circuit on the left of Figure 1, where a dual power supply consists of a positive power supply and an equally voltage negative power supply. Generally, it is positive or negative 15V, positive or negative 12V, and positive or negative 5V, which are also commonly used. The input voltage and output voltage are both given by the reference ground, including the maximum swing amplitude Vom of the positive and negative voltages and the maximum output swing amplitude.
The power pin of the operational amplifier in a single power supply circuit is connected to a positive power source and ground. Connect the positive power pin to VCC+, or connect the ground or VCC - pin to GND. Divide the positive voltage into half and connect it as a virtual ground to the input pin of the operational amplifier. At this time, the output voltage of the operational amplifier is also the virtual ground voltage. The output voltage of the operational amplifier is centered around the virtual ground and the amplitude is within Vom. Some new operational amplifiers have two different maximum output voltages and minimum output voltages. The data manual for this type of operational amplifier will specifically specify Voh and Vol. It should be noted that many designers casually use virtual ground to refer to input and output voltages. However, in most applications, the input and output are based on the reference power source ground, so designers must add DC isolation capacitors at the input and output points to isolate the DC voltage between virtual ground and ground.
Usually, the voltage supplied by a single power source is 5V, and the output voltage swing of the operational amplifier will be lower. In addition, the current power supply voltage of the operational amplifier can also be 3V or even lower. For this reason, the operational amplifiers used in single power supply circuits are mostly Rail To Rail operational amplifiers, which eliminates the loss of dynamic range. It should be noted that both input and output may not be able to withstand the voltage of Rail To Rail. Although the device is specified as Rail to Rail, if the output or input of the operational amplifier does not support Rail to Rail, voltage approaching the input or output voltage limit may degrade the functionality of the operational amplifier. Therefore, it is necessary to carefully refer to the data manual to ensure that both input and output are Rail to Rail. This is the designer's obligation to ensure that the system's functionality does not degrade.
