The name of the precision full-wave rectifier circuit in the figure is the name of the person's life. It is only for the sake of distinction. Unless otherwise specified, the gain is designed according to 1.
Figure 7,8,9 three circuits, when the output of the op amp A1 is positive, the negative feedback of A1 is formed by the composite amplifier formed by the diode D2 and the op amp A2. Due to the compound (product) effect of the two op amps, It is possible that the gain of the loop is too high and it is prone to oscillation. Some precision full-wave circuits are not entered, such as high-impedance type. There is also a way to connect the non-inverting input of A2 to the inverting input of A1. In fact, this type of high-impedance type The principle is the same, there is no special collection, other output using A1 only a diode is not included, because when this diode is cut off, A1 is in an open-loop state.
Conclusion: Although there are ten kinds of precise full-wave circuits here, careful analysis shows that there are not many excellent ones. To be exact, there are only three types, that is, the first three types.
Although the classic circuit of Figure 1 has a large number of matching resistors, it can be completely implemented with 6 equivalent resistors R. The resistor R3 can be connected in parallel with two Rs. The gain can be adjusted by R5, and the gain can be greater than 1 or less than 1. The advantage is that it can be capacitively filtered on R5.
The advantage of the circuit in Figure 2 is that the matching resistor is small, as long as a pair of matching resistors is enough.
The advantage of Figure 3 is the high input impedance. Several other types, some in the D2 conduction half cycle, through the A2's composite negative feedback A1, for some op amps will appear self-excited. Some two half wave input Impedance is not equal, which requires high signal source. Although the two single op amp types can achieve the purpose of rectification, the input/output characteristics are all very poor. It requires input/output to add followers or non-inverting amplifier isolation. Each circuit has its own Its design features, hope that we can draw useful from its clever design of the circuit, such as the design of a single-wave full-wave circuit, the design of a composite feedback circuit, are very useful design ideas and methods, if you can put the various diagrams Circuit principles will benefit from analyzing and deriving each formula.
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