CN104917480A - Adjustable stepping passive attenuation circuit for test of power line carrier - Google Patents

Abstract

The invention relates to an adjustable stepping passive attenuation circuit for test of a lower line carrier. A low pass filter part and a high frequency signal attenuation part are connected parallelly so as to form the adjustable stepping passive attenuation circuit. The low pass filter part adopts a multistage longitudinal redundancy check (LRC) low pass filter circuit, thereby shielding external interference. The high frequency signal attenuation part comprises a multistage pi type/T type/ bridge T type balance attenuation network. All the three network types belong to a symmetrical attenuation network and are mainly used for signal attenuation. While a 220V power supply interference signal is shielded, stepping attenuation regulation and control on the high frequency power line carrier signal is realized. The same attenuation degree of general carrier frequency bands is realized and the attenuation degree is highly consistent.

Description

A kind of adjustable stepping passive attenuation circuit for power line carrier test

Technical field

The present invention relates to a kind of passive attenuation circuit, be specifically related to a kind of adjustable stepping passive attenuation circuit, be mainly used in power line carrier test.

Background technology

The test of power line carrier is undertaken by attenuator.Sensitivity is an important test index.The advantage such as passive attenuator has that Insertion Loss is little, impedance matching good, simple to operate and price is low.Chinese invention patent " circuit of power line carrier signal adjustable attenuator ", in low-pass filtering design, achieves bidirectional filtering with effect.Have employed knob governor motion in high frequency signal attenuation part, easily wear and tear.Its degree of decay cannot intuitively show, and because its continuously adjustabe causes precision poor, needs complicated test step to determine the degree of decay and attenuation accuracy.Because they are different to the different carrier frequencies degree of decay, cause complex operation.

Summary of the invention

Technical problem to be solved by this invention is, provides a kind of adjustable stepping passive attenuation circuit for power line carrier test, while shielding 220V power supply disturbance signal, realizes regulating and controlling the stepped attenuation of high-frequency electrical line of force carrier signal; The identical degree of decay is realized to general carrier wave frequency range, and consistency is higher.

Technical scheme of the present invention is as follows:

For an adjustable stepping passive attenuation circuit for power line carrier test, it is characterized in that it is made up of low-pass filtering part and high frequency signal attenuation part in parallel;

Low pass filtering section divides the inductance L 1 ~ Ln comprising and being connected successively to ac output end mouth Lout, Nout by ac input end mouth Lin, Nin, is parallel with electric capacity C1 ~ Cn and the resistance R1 ~ Rn of series connection mutually between the corresponding node between inductance;

High frequency signal attenuation part comprises the electric capacity Ch1 and electric capacity Ch2 that are connected successively to ac output end mouth Lout, Nout by ac input end mouth Lin, Nin; Multistage balance attenuation network is connected with between electric capacity Ch1 and electric capacity Ch2; Described balance attenuation network comprises π type balance attenuation network, the one in T-shaped balance attenuation network and bridge T-shaped balance attenuation network or two or more.

Preferably, protection fuse or thermistor is added, for preventing short circuit at the input of Lin or Nin.

Preferably, in high frequency signal attenuation partial circuit, π type, the T-shaped and T-shaped resistor network of bridge separately input and output impedance be set to identical numerical value;

Computing formula for resistance Rh1 and Rh2 forming π type impedance matching network circuit is as follows:

Wherein D is attenuation multiple, unit dB; Z _{characteristic impedance}get 50 Ω;

Computing formula for resistance Rh1 and Rh2 forming T-shaped impedance matching network circuit is as follows:

Wherein D is attenuation multiple, unit dB; Z _{characteristic impedance}get 50 Ω;

Computing formula for resistance Rh1, Rh2 and Rh3 of forming bridge T-shaped impedance matching network circuit is as follows:

Wherein D is attenuation multiple, unit dB; Z _{characteristic impedance}get 50 Ω.

Good effect of the present invention is: circuit of the present invention adopts unidirectional filtering, and such filter effect is better, also saves cost.And adopt stepped attenuation design, adopt some fixing degree of decay set-points, attenuation value can be known very intuitively.The present invention can realize the identical degree of decay to certain frequency range, and versatility is high.Substantially identical to a few MHZ degree of decay from 100KHZ.

Accompanying drawing explanation

Fig. 1 is the artificial circuit of low-pass filtering partial circuit.

Fig. 2 is the simulation result of low-pass filtering partial circuit.

Fig. 3 is the characteristic impedance test circuit of low pass isolated part.

Fig. 4 is π type impedance matching network elementary cell, and wherein left side is unbalanced type, and right side is balanced type.

Fig. 5 is T-shaped impedance matching network elementary cell, and wherein left side is unbalanced type, and right side is balanced type.

Fig. 6 is the T-shaped impedance matching network elementary cell of bridge, and wherein left side is unbalanced type, and right side is balanced type.

Fig. 7 is π type balance attenuation device circuit and parameter.

Fig. 8 is T-shaped balance attenuation device circuit and parameter.

Fig. 9 is bridge T balance attenuation device circuit and parameter.

Figure 10 is π type balance attenuation device circuit simulation result.

Figure 11 is T-shaped balance attenuation device circuit simulation result.

Figure 12 is bridge T-shaped balance attenuation device circuit simulation result.

Figure 13 is the relation between the stepped attenuation device degree of decay and frequency.

Figure 14 is button design, totally four tunnels, and two-way is often opened, and two-way is normally closed.

Figure 15 is the circuit theory diagrams simultaneously comprising π type, the T-shaped and T-shaped three types attenuation network of bridge.

Embodiment

The present invention is further illustrated below in conjunction with the drawings and specific embodiments.

Circuit of the present invention is made up of low-pass filtering part and high frequency signal attenuation part in parallel, sees Figure 15.

Low-pass filtering part is made up of n level LCR, and this circuit seals in Ln inductance successively by Lin and Nin, make L, N two line form a kind of balanced structure, between multistage inductance, be incorporated to electric capacity Cn and resistance Rn.Add resistance R at the beginning and end place of circuit, since regulation quality factor Q value, intergrade eliminates resistance R, because its effect is less.First order resistance and afterbody resistance can be used to carry out impedance matching.Low-pass filtering part artificial circuit is shown in Fig. 1, and simulation result is shown in Fig. 2.

High frequency signal attenuation part is made up of multistage π type balance attenuation network, this circuit seals in electric capacity Ch1 and electric capacity Ch2 successively by Lin, Nin, and between electric capacity Ch1 and electric capacity Ch2, string is incorporated to the T-shaped balance attenuation network of multistage π type/T-shaped/bridge be made up of resistance Rhm and resistance Rh (m+1).

The π type of high frequency signal attenuation part, T-shaped and bridge T-shaped balance attenuation network is mutually general, and an attenuation network also can comprise this three types simultaneously.

Protection fuse or thermistor is added, to prevent short circuit in the front end of Lin or Nin.

The node of low-pass filtering part between Lin and Nin, inductance and electric capacity Cn and resistance Rn position interchangeable.

LCR structure at different levels and position interchangeable.

Between the resistor network of high frequency signal attenuation part, position is interchangeable.

The characteristic impedance of whole power line carrier signal attenuating device is set to 50 general Ω or other particular/special requirement values.

The resistance r of low-pass filtering part Lin input is the internal resistance of 220V alternating current source, is present in whole attenuation model, but is not present in attenuating device.

As Fig. 7, the resistance r accessed by ac input end mouth Lin is insulating power supply internal resistance, about 100 Ω.Ac input end mouth Lin, Nin and the low-pass filtering part between ac output end mouth Lout, Nout are made up of seven grades of LRC filter circuits.Inductance L 1 ~ L7 is sealed in successively respectively, value 680uH to ac output end mouth Lout, Nout by ac input end mouth Lin, Nin.Electric capacity C1 ~ the C7 of series connection mutually in parallel successively between the corresponding node between inductance and resistance R1 ~ R7, wherein electric capacity C1 ~ C6 value 220nF, electric capacity C7 value 470nF, resistance R 1 and R7 value 50 Ω, resistance R 2=R 6 value 20 Ω, resistance R3, R4 and R5 value 0 Ω.

The multistage π type balance attenuation network of composition.The relation of low pass buffer circuit degree of decay D and frequency f is as follows:

Approximate formula $D=20log\left|\frac{U_O}{U_I}\right|=20{\Σ}_{i=1}^n\left\{\log \left|\frac{R_i+\frac{1}{j2{\mathrm{\πfC}}_i}}{j2\mathrm{\π}f\left(2L_i\right)+R_i+\frac{1}{j2{\mathrm{\πfC}}_i}}\right|\right\},$ Unit dB.

The characteristic impedance computational methods of low pass isolated part, test circuit adopts Fig. 3, and power designs is about 10W.The resistance of load is 5K, and when power designs is larger, degree of decay D needs to consider load resistance.Computing formula is as follows:

1., precise calculation is:

2., approximate formula is: Z _{characteristic impedance}=Z _r+ Z _c, during high frequency, be approximately equal to 0.

High frequency signal attenuation partial circuit designs: the T-shaped resistor network of π type, T-shaped and bridge requires that input-output characteristic impedance is consistent, so input and output impedance need be arranged to identical numerical value.

π type impedance matching network electricity routing resistance Rh1 and Rh2 composition, see Fig. 4, computing formula is as follows:

Wherein D is attenuation multiple, unit dB.Z _{characteristic impedance}generally get 50 Ω, for impedance matching and test.

T-shaped impedance matching network electricity routing resistance Rh1 and Rh2 composition, see Fig. 5, computing formula is as follows:

Wherein D is attenuation multiple, unit dB.Z _{characteristic impedance}generally get 50 Ω, for impedance matching and test.

Bridge T-shaped impedance matching network electricity routing resistance Rh1, Rh2 and Rh3 composition, see Fig. 6, computing formula is as follows:

Wherein D is attenuation multiple, unit dB.Z _{characteristic impedance}generally get 50 Ω, for impedance matching and test.According to aforesaid theory analysis and calculating, input to Lout, Nout from AC port Lin, Nin and export, low-pass filtering part is all-pass for AC power frequency signal, and the attenuation rate D LF of corresponding 20kHz signal reaches-71dB.

High frequency signal attenuation part is incorporated to π type balance attenuation network successively from ac input end mouth Lin, Nin to ac output end mouth Lout, Nout.The stepping degree of decay is 2dB, 4dB, 8dB, 16dB, 20dB, 20dB and 20dB, altogether 90dB.By characteristic impedance be 50 Ω calculate, data are as follows:

Three kinds of lattice networks and concrete numerical value are shown in Fig. 7, Fig. 8 and Fig. 9 respectively.

π type balance attenuation device circuit simulation result is tested out as Figure 10 by simulation software Multisim, T-shaped balance attenuation device circuit simulation result is as Figure 11, bridge T-shaped balance attenuation device circuit simulation result is as Figure 12, balance attenuation device stepping decay simulation result is as Figure 13, and the stepping degree of decay is 20dB, 20dB, 20dB, 16dB, 8dB, 4dB and 2dB.Press-key structure part designs with reference to Figure 14, is used for carrying out the step-wise adjustment of the degree of decay.

Claims (3)

1., for an adjustable stepping passive attenuation circuit for power line carrier test, it is characterized in that it is made up of low-pass filtering part and high frequency signal attenuation part in parallel; Low pass filtering section divides the inductance L 1 ~ Ln comprising and being connected successively to ac output end mouth Lout, Nout by ac input end mouth Lin, Nin, is parallel with electric capacity C1 ~ Cn and the resistance R1 ~ Rn of series connection mutually between the corresponding node between inductance; High frequency signal attenuation part comprises the electric capacity Ch1 and electric capacity Ch2 that are connected successively to ac output end mouth Lout, Nout by ac input end mouth Lin, Nin; Multistage balance attenuation network is connected with between electric capacity Ch1 and electric capacity Ch2; Described balance attenuation network comprises π type balance attenuation network, the one in T-shaped balance attenuation network and bridge T-shaped balance attenuation network or two or more.

2. the adjustable stepping passive attenuation circuit for power line carrier test according to claim 1, is characterized in that: add protection fuse or thermistor, for preventing short circuit at the input of Lin or Nin.

3. power line carrier signal attenuating device according to claim 1, is characterized in that: in high frequency signal attenuation partial circuit, π type, the T-shaped and T-shaped resistor network of bridge separately input and output impedance be set to identical numerical value; Computing formula for resistance Rh1 and Rh2 forming π type impedance matching network circuit is as follows:

Wherein D is attenuation multiple, unit dB; Z _{special impedance}get 50 Ω;

Computing formula for resistance Rh1 and Rh2 forming T-shaped impedance matching network circuit is as follows:

Wherein D is attenuation multiple, unit dB; Z _{special impedance}get 50 Ω;

Computing formula for resistance Rh1, Rh2 and Rh3 of forming bridge T-shaped impedance matching network circuit is as follows:

Wherein D is attenuation multiple, unit dB; Z _{special impedance}get 50 Ω.