JPH0336093Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an average value rectifying device, and an object of the present invention is to provide an average value rectifying device that has high input impedance and can extract maximum output.

Generally, an average value rectifier uses a capacitor in the input circuit to cut the DC component, as shown in Figure 1.
_C1 is connected, and when amplifying the signal, an amplifier A is connected to the output side of the capacitor. In this case, a resistor R is connected to define the operating center potential of the amplifier A, but this resistor has the disadvantage that the input impedance of the amplifier A is lowered.

The present invention was devised in view of these points, and has realized an average value rectifier that has a high input impedance and can extract maximum distortion-free output by making effective use of the power supply voltage.

FIG. 2 is a circuit diagram of an embodiment of the device of the present invention. In FIG. 1, BS is a bootstrap circuit and FL is an average value rectifier circuit. In the bootstrap circuit BS, OP-1 is an operational amplifier,
Its (-) input terminal and output terminal are connected to form a voltage follower, and a capacitor C ₁ is connected between the signal input terminal IN and the (+) of OP-1.
is connected. Also, (+) of this OP-1
One end of a resistor _R1 is connected to the input terminal, and the other end of the resistor _R1 is connected to the output terminal of OP-1 via a bootstrap capacitor _C2 . V ₊ and
V _- is a positive and negative voltage source, respectively, R ₂ and R ₃ are resistive elements, both resistors are connected in series, and the connecting point a of the capacitor C ₂ and the resistor R ₁ is connected to the connecting point.

In the average rectifier circuit FL, OP-2 is an operational amplifier, D ₁ and D ₂ are diodes, R ₄ and R ₅ are resistive elements, C ₃ and C ₄ are capacitors, and OUT is an output terminal. The output terminal of the operational amplifier OP-1 constituting the bootstrap circuit BS is connected to the (-) input terminal of _OP2 through a series circuit of a capacitor _C3 and a resistor _R4 . A diode D ₁ is connected between the (−) input terminal and the output terminal of OP ₂ , and the output terminal of OP ₂ is connected to the output terminal OUT via the diode D ₂ . Also, the (-) of OP-2 and the diode
A parallel circuit of a capacitor _C4 and a feedback resistor _R5 is connected between the output terminals of _D2 .

The operation of the average value rectifier according to the present invention will be explained as follows. The input signal _Vio applied from the input terminal IN has its DC component removed by the capacitor _C1 , and is applied to the operational amplifier OP-1 constituting the bootstrap circuit BS. In this case, as the power supply voltage of OP ₁ , resistor R ₂ ,
Since positive and negative voltages V ₊ and V _- are applied via R ₃ , the operating center voltage of OP-1 is determined by R ₂ and R ₃ , and the absolute values of V ₊ and V _- are equal to R ₂ When = R ₃ , OP-1 operates at the center of positive and negative voltages. The bootstrap circuit BS in which the power supply voltage of the operational amplifier _OP1 is determined in this way is bootstrapped by the capacitor _C2 as is well known, and has a high input impedance. The output of the bootstrap circuit BS is applied to an operational amplifier OP-2 constituting an average value rectifier circuit FL. This average value rectifier circuit is a known one, in which the input signal Vin′ passing through the bootstrap BS is half-wave rectified by diodes D ₁ and D ₂ , and the feedback resistor R ₅
By inserting and connecting the capacitor _C4 in parallel with the input signal, the output voltage _V0 of OP-2 is
The average value of Vin' is rectified. This average value rectified output voltage V ₀ is taken out from the output terminal OUT.

In the average value rectifier according to the present invention, the input signal is input by the bootstrap circuit BS.
Since Vin is bootstrapped, it has a high input impedance, and since the operating center voltage of operational amplifier OP-1 can be centered on the power supply voltage due to the ratio of resistors R ₂ and R ₃ , it can be used up to a larger input voltage. It will function without distortion. The output of operational amplifier OP-1 operating in this manner is applied to operational amplifier OP-2 having an average value rectification function. Therefore, in the device of the present invention, it is possible to obtain an average value rectifier that has a high input impedance and can increase the maximum output due to effective use of the power supply voltage. In this way, in the device of the present invention, the output swing of the operational amplifier OP-2 is reduced, so the power supply voltage V _±
It has the characteristic of operating even when the temperature is low.

FIG. 3 is a block diagram of another embodiment of the present invention. In Figure 3, the output of operational amplifier OP-2, which constitutes the average value rectifier, is connected to the common COM through a series circuit of resistors R ₃ and R ₂ , and
The connection point between R ₂ and R ₃ is connected to the connection point a between the resistor R ₁ and the capacitor C ₂ of the bootstrap circuit BS. There are cases where you want to level shift the output voltage V ₀ in the positive direction with respect to the common COM, but in such a case, if you connect it as shown in Figure 3.
The level of the operational amplifier OP-1 is shifted in accordance with the increase in Vin∝V ₀ . In the circuit of FIG. 3, there is no level shift at Vin0, and the leakage current i of the capacitor _C3 disappears, so there is an advantage that accuracy is improved when Vin is close to zero.

In addition, in Figures 2 and 3, the diode
If the connection direction of D ₁ and D ₂ is reversed, the output voltage V ₀ will have negative polarity.

As described above, according to the present invention, an average value rectifier having a high input impedance and capable of extracting maximum output can be obtained with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional device, and FIGS. 2 and 3 are circuit diagrams of embodiments of the device of the present invention. BS...Bootstrap circuit, _C2 ...bootstrap capacitor, FL...average rectifier circuit.

Claims (1)

[Claim for Utility Model Registration] A bootstrap capacitor, one end of which is connected to the output end of an operational amplifier to which an input signal is applied via a capacitor for cutting DC components, and the other end of this capacitor being connected to the connection point. A bootstrap circuit having a pair of resistors R2 and R3 that are connected and set the operating center voltage of the operational amplifier according to their resistance ratio, and between the input and output terminals of the operational amplifier to which the output of this bootstrap circuit is applied, and the output terminal. an average value rectifier circuit comprising diodes D1 and D2 connected to the diodes D1 and D2, respectively, and a resistor R5 and a capacitor C4 connected between the input terminal of the operational amplifier and the other end of the diode D2; Rectifier.