JPH05236751A - AC-DC converter - Google Patents

Abstract

PURPOSE:To obtain a DC signal having high S/N ratio by passing each unit signal, separated at a signal separating section, through a band filter having passing band characteristics corresponding to respective frequency components and then rectifying the unit signal. CONSTITUTION:A microprocessor 7 drives an SW based on a synchronizing pulse signal ACp and performs switching control of output systems from a multiplexer 6 to separate respective signal components (a), (b), (c), as unit signals ACa. ACb, ACc, from an AC signal ACin and then delivers thus separated unit signals ACa, ACb, ACc to the output systems of the multiplexer 6. These unit signals ACa, ACb, ACc are connected through buffer amplifiers BA2, BA3, BA4 with respective bandpass filters 3. The bandpass filter 3 is set at such band as the frequency component of each unit signal ACa, ACb, ACc is passed selectively. According to the constitution, white noise is eliminated from AC output signals ACa, ACb, ACc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC / DC converter, and more particularly to an AC / DC converter suitable for converting a complex AC signal composed of a plurality of signals into a DC signal.

[0002]

2. Description of the Related Art For example, an output signal of a detection unit of a moisture meter for measuring a moisture content of paper in a papermaking process is synthesized by three kinds of signals a, b, c having periodicity as shown in FIG. It is _in the form of a complex AC signal AC _{in with} a white noise component superimposed. Conventionally, in converting the three types of signals a, b, and c that constitute such an AC signal AC _in into DC signals DC _a , DC _b , and DC _c for each signal,
As shown in FIG. 4, three sample hold circuits S / H _a , S / H _b , and S / H _c connected in parallel are used, and these sample hold circuits S / H _a , S / H _b , and S / H are used. the _c signals a, b, timing _t a1, t synchronized with the period of c
Driven by _b1 , t _c1 , t _a2 , t _b2 , t _c2 , ..., And sample holding was performed.

[0003]

However, when the white noise is superimposed on the AC signal AC _in as described above, the sample and hold circuits S / H _a and S are included because the white noise is also sample-held. /
White noise is also included in the output signals of H _b and S / H _c , and the S / N ratio decreases. That is, the S / N ratio of the conventional circuit configuration is determined by the input signal.

The present invention has been made in view of the above problems, and an object thereof is to provide an AC / DC converter having a high S / N ratio.

[0005]

SUMMARY OF THE INVENTION The present invention which solves such a problem includes a signal separating section for separating each signal component as a single signal from an AC signal synthesized by a plurality of types of signals having periodicity, A plurality of bandpass filters that selectively pass the frequency component of each single signal output from the signal separation unit, and a rectification unit that converts an AC signal output from the bandpass filter into a DC signal It is characterized by being done.

[0006]

The single signals separated by the signal separation section have constant frequencies. Therefore, by adding each of these single signals to a bandpass filter having a pass band characteristic corresponding to each frequency component, an AC signal from which noise components have been removed can be obtained. Then, by rectifying the AC signal by the rectifying unit, a DC signal having a high S / N ratio can be obtained.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram of the principle of the present invention.
In the figure, reference numeral 1 is an input terminal of an AC signal AC _in that is composed of a plurality of types of signals a, b, and c having periodicity, and is connected to the signal separation unit 2. The signal separation unit 2 uses the AC signal A
Each signal component a, b, c from C _{in is} converted into a single signal AC _a , A
Separated as C _b and AC _c . Reference numeral 3 denotes a bandpass filter, which outputs each single signal A output from the signal separation unit 2.
The frequency components of C _a , AC _b , and AC _c are selectively passed. Reference numeral 4 denotes a rectification unit, which is an AC signal AC _a ′, AC _b ′, AC _c output from each band pass filter 3.
′ Is converted into DC signals DC _a , DC _b , DC _c .

FIG. 2 is a circuit diagram showing a specific example of FIG.
A sync pulse generator 5 is connected to the input terminal 1, and one end of a capacitor C is also connected. The other end of the capacitor C is connected to the ground via the switch SW and is also connected to the multiplexer 6 via the buffer amplifier BA ₁ . The AC signal AC _in is clamped to 0V by the capacitor C and the switch SW, and the buffer amplifier B
Impedance conversion is performed at A1 and input to the multiplexer 6. The synchronization pulse generator 5 generates a pulse signal AC _p synchronized with the AC signal AC _in to generate a pulse signal AC _p.
Output to the pulse input terminal of.

The drive coil of the switch SW is connected to the I / O terminal of the microprocessor 7, and the multiplexer 6 is connected via the data bus DB. That is,
The microprocessor 7 drives the switch SW based on the pulse signal AC _p and controls the output system of the multiplexer 6 to be switched. The output system of the multiplexer 6, the AC signal _{AC in} the signal from the component a, b, c is a single signal _{AC a,} AC b, are separated and output as AC _c. These single signals AC _a , AC _b and AC _c are connected to the respective band pass filters 3 via buffer amplifiers BA ₂ , BA ₃ and BA ₄ . The band pass filter 3 of each system is configured to receive each single signal A input to each.
The bands are set to pass selectively the frequency components of C _a , AC _b , and AC _c . As a result, the AC signal AC _a ′, A output from each band pass filter 3
C _b ′ and AC _c ′ are high-purity signal components in which white noise components are almost removed.

As the rectifying unit 4, for example, a diode rectifier is used.

[0011]

As described in detail above, according to the present invention, the band width of the signal can be made extremely narrow as compared with the conventional configuration using the sample and hold circuit, so that the S / N ratio of the input AC signal is increased. It is possible to obtain a DC signal having a high S / N ratio even if the value is poor.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a diagram showing a specific circuit example of FIG.

FIG. 3 is a waveform example diagram of a complex AC signal composed of a plurality of signals.

FIG. 4 is a block diagram showing an example of a conventional AC-DC converter.

[Explanation of symbols]

 1 Input Terminal 2 Signal Separation Section 3 Band Pass Filter 4 Rectifier Circuit

Claims (1)

[Claims] 1. A signal separation unit for separating each signal component as a single signal from an AC signal composed of a plurality of types of signals having periodicity, and a frequency component of each single signal output from the signal separation unit. An AC-DC converter, comprising: a plurality of band-pass filters that selectively pass through the filter; and a rectifying unit that converts an AC signal output from the band-pass filter into a DC signal.