CN1222012A - Nonlinearity compensation of laser diode and other semiconductor diodes - Google Patents

Abstract

A high-linearity light source comprising a first semiconductor diode (e.g., a light-source diode such as a laser diode or a light-emitting diode, or a light-receiving diode such as a photodetector) and a nonlinearity compensation network with a second, compensation, semiconductor diode is provided. The first and second diodes are connected in an antiparallel configuration with either an A.C. signal source (for light emission) or a load (for light receiving) and in separated D.C. bias paths.

Description

The nonlinear compensation of laser diode and other semiconductor diodes

The present invention relates to modulate semiconductor diode, particularly relate to the nonlinear distortion that reduces the semiconductor diode light source.

Along with increase to the optical communication demand, to better performance is arranged, more the demand of the optical communication technique of low distortion is also increasing.

The core of optical transmission system is at light source, and light-emitting diode (LED) and laser diode are generally these systems light is provided.Yet the non-linear junction capacitance of the inherence of these devices has caused undesirable harmonic wave and mutual modulation, and this has just caused distortion, has reduced properties of product.

In optical transmission system, the high linearity of light source and low noise are key factors.People attempt by improving the light source manufacturing technology, reduce predistortion and using FEEDBACK CONTROL to improve the linearity of light source.Yet these methods have caused the increase of cost and have strengthened the difficulty of manufacturing process.The present inventor reduces secondary and third order distortion harmonic wave by the anti-series of using diode in an invention (US 4,032,802) formerly, thereby improves the linearity.

The present invention utilizes the inverse parallel (wherein diode reverse biased) to semiconductor diode, improve present inventor system early with anti-series structure reduction distortion, reduced DC consumption, low frequency noise and heating to reduce harmonic distortion and to compare with the anti-series system.

The invention provides a non-linear compensation circuit, use with the A.C. signal source.In an optimum embodiment, this circuit comprises first and second semiconductor diodes, and these two diodes connect into the inverse parallel form, and in parallel with signal source.These semiconductor diodes have the first and second voltage variable capacitance characteristics respectively.A DC power supply circuit provides first and second bias voltages to this first and second semiconductor diode respectively.By regulating these semi-conductive corresponding biasings, circuit capacitance also can be adjusted, and to reduce undesirable harmonic wave, improves the linearity of circuit.

In another optimum embodiment, first semiconductor diode is a light source diode, and second semiconductor diode is a compensation diode, and power supply adds reverse bias to the compensation diode, adds forward bias to the light source semiconductor diode simultaneously.This bias mode only needs few direct current power consumption.And power supply only produces few heat in circuit, avoided the distortion relevant with heat.

In another optimum embodiment, first power supply provides biasing to the light source semiconductor diode, and simultaneously, second source provides biasing to compensation semiconductor's diode.The same among the same embodiment of this arrangement, the advantage of hanging down straight power consumption is arranged.And first and second power supplys provide isolated mutually direct current biasing shunt, can allow compensation semiconductor's diode is carried out independently bias-adjusted under the situation of the performance that does not influence the light source diode.

Fig. 1 is the schematic diagram of an optimum embodiment of the present invention;

Fig. 2 is the equivalent circuit diagram of semiconductor diode;

Fig. 3 is a radio frequency of the present invention (RF)/interchange (A.C.) equivalent circuit diagram;

Fig. 4 is a pc equivalent circuit figure of the present invention;

Fig. 5 is the schematic diagram of one second preferred embodiment of the present invention; With

Fig. 6 is the schematic diagram of one the 3rd embodiment of the present invention.

Fig. 1 shows a preferred embodiment of photoelectric circuit 10 of the present invention.The positive pole 11 of light source semiconductor diode 12 is connected with ground 38.The negative pole 13 of light source semiconductor diode 12 links to each other by the positive pole 15 of second electric capacity 30 with compensation semiconductor diode 14.The negative pole 17 of compensation semiconductor's diode 14 is connected to ground 38 by the 3rd electric capacity 32.

Fig. 2 shows the light source semiconductor diode 12 that is applied with junction voltage 41 and the semiconductor diode equivalent electric circuit 40 of compensation semiconductor's diode 14.The bonding line of diode has caused first and second inductance 42,44.Junction capacitance 46 depends on the structure of tying depletion layer.Junction resistance 48 is represented junction resistance and diffusion.

Refer again to Fig. 1, those of ordinary skills will find out that this connection is to have the light source semiconductor diode of A.C. signal source 20 12 and compensation semiconductor's diode 14 reverse parallel connections, and Fig. 3 shows the ac equivalent circuit 50 of photoelectric circuit 10.Inverse parallel connected mode shown in Fig. 3 has formed a non-linear compensation circuit (NCN) 51.Light source semiconductor diode 12 can be to comprise, but is not limited in the one of several of laser diode (LD) and light-emitting diode (LED).Compensation semiconductor's diode 14 also can be one of any several forms, as long as it has the required equivalent electric circuit that discusses below.

Get back to Fig. 1, the preferred embodiment comprises a biasing circuit, and it comprises that discrete direct current biasing is added on light source semiconductor diode 12 and the compensation semiconductor's diode 14, and all is isolated with A.C. signal source 20.First bias source 16 provides direct current biasing for light source semiconductor diode 12.Second electric capacity 30 completely cuts off first bias source 16 on the left side of second electric capacity 30 from way circuit, particularly the left side of second bias source 18.This completely cutting off easilier in the straight equivalent electric circuit of photoelectric circuit 10 find out, furtherly, and at the straight biasing equivalent electric circuit 54 (as shown in Figure 4) of light source diode 12, in the middle of, easilier find out.Directly setover equivalent electric circuit 52 as can be known from the compensation diode as can be seen in the middle of Fig. 4, and second bias source 18 provides direct current biasing for compensation semiconductor's diode 14.Get back to Fig. 1 again, second bias source 18 provides a reverse bias for compensation semiconductor's diode 14, and this biasing can be adjusted by regulating variable resistor 34.First, second and the 3rd inductance 22,24,26 are used for first and second bias sources 16,18 and A.C. signal source 20 isolated opening, thereby obtain equivalent electric circuit Fig. 3 and Fig. 4.

Light source semiconductor diode 12 in the ac equivalent circuit 50 (Fig. 3) and compensation semiconductor's diode 14 usefulness are partly led after diode equivalent circuit 40 replaces, analyzed Figure 50, demonstrate the possibility that reduces harmonic distortion.The electric capacity of a diode is V at institute's biasing _OWhen being V with add modulation small signal, its expression formula is: $C=\frac{C_0}{{(\mathrm{\θ}-V_0)}^n}{(1-\frac{V}{\mathrm{\θ}-V_0})}^{-n}=K_0+K_{1}v+K_2{v}^2+K_3{v}^3+\·\·\·----\left(1\right)$ Wherein:

C _OIt is a constant that is directly proportional with junction capacitance 46;

θ represents the disintegration voltage of diode; With

N is the relevant number of a diode junction place dopant profiles. $K_0=\frac{C_0}{{(\mathrm{\θ}-V_0)}^n}----\left(2\right)$ $K_1=\frac{{\mathrm{nK}}_0}{\mathrm{\θ}-V_0}---\left(3\right)$ $K_2=\frac{n(n+1)K_0}{2{(\mathrm{\θ}-V_0)}^2}----\left(4\right)$ $K_3=\frac{n(n+1)(n+2)K_0}{6{(\mathrm{\θ}-V_0)}^3}----\left(5\right)$

Equation (3), (4) and (5) are represented secondary, three times and four distortions respectively.Wherein, second-order distortion is maximum single component in distortion.If the inferior distortion of this grade can be eliminated or reduce to a circuit, and also reduce the inferior distortion of other grades if possible, then harmonic distortion in the photoelectric circuit 10 and intermodulation product will correspondingly reduce.

In the non-linear compensation circuit 51 of the present invention (as shown in Figure 3), compensation semiconductor's diode 14 and light source semiconductor diode 12 are connected into the inverse parallel relation, be connected with A.C. signal source 20 again.Biasing circuit provides a direct current biasing for each diode.Anyly be added to incremental voltage V on the diode, will near their bias points separately, modulate respectively the electric current that flows through diode by A.C. signal source 20.Because this kind inverse parallel, A.C. signal source 20 equal and opposite in directions, direction is exerted one's influence to the voltage on light source semiconductor diode 12 and the compensation semiconductor's diode 14 on the contrary.In optimum embodiment of the present invention, light source semiconductor diode 12 is forward bias, and compensation semiconductor's diode is a reverse bias.

In an optimum embodiment of the present invention, light source semiconductor diode 12 and compensation semiconductor's diode 14 all are the semiconductor diodes with above equivalent electric circuit of discussing.Therefore, the electric capacity of light source semiconductor diode 12 and compensation diode 14 can be expressed as:

C ₁=K ₁₀-K ₁₁V+K ₁₂V ²-… (6)

C ₂=K ₂₀+K ₂₁V+K ₂₂V ²+… (7)

Wherein, C ₁The electric capacity of=light source semiconductor diode 12

C ₂The electric capacity of=compensation semiconductor diode 14.

In conjunction with equation (6) and (7), we can obtain total capacitance and are:

C _∑=C ₁+C ₂=K _Σ1-K _∑2V+K _∑2V ²…… (8)

Wherein, $K_{\mathrm{\&Sigma;}0}=\frac{C_{10}}{{(\mathrm{\&theta;}-V_{10})}^n}+\frac{C_{20}}{{(\mathrm{\&theta;}-V_{20})}^n}----\left(9\right)$ $K_{\mathrm{\&Sigma;}1}=\frac{\mathrm{<figure-callout\; id="10"\; label="n\; K"\; filenames="A9810052400111.png"\; state="\{\{state\}\}">n</figure-callout>}{K}_{}{}_{10}}{\mathrm{\&theta;}-V_{10}}-\frac{\mathrm{<figure-callout\; id="20"\; label="n\; K"\; filenames="A9810052400111.png,A9810052400131.png"\; state="\{\{state\}\}">n</figure-callout>}{K}_{}{}_{20}}{\mathrm{\&theta;}-V_{20}}----\left(10\right)$ $K_{\mathrm{\&Sigma;}2}=\frac{n(n+1){\mathrm{<figure-callout\; id="10"\; label="K"\; filenames="A9810052400111.png"\; state="\{\{state\}\}">K</figure-callout>}}_{10}}{2{(\mathrm{\&theta;}-V_{10})}^2}+\frac{n(n+1){\mathrm{<figure-callout\; id="20"\; label="K"\; filenames="A9810052400111.png,A9810052400131.png"\; state="\{\{state\}\}">K</figure-callout>}}_{20}}{2{(\mathrm{\&theta;}-V_{20})}^2}----\left(11\right)$

The bias voltage V of light source semiconductor diode 12 and compensation semiconductor 14 among the present invention ₁₀And V ₂₀Can be conditioned.Therefore, by with K _{∑ 1}Be adjusted to 0, can easily the quadratic nonlinearity distortion be eliminated fully (seeing equation 10).

From equation (1) and (5), if we make $\frac{{\mathrm{<figure-callout\; id="10"\; label="K"\; filenames="A9810052400111.png"\; state="\{\{state\}\}">K</figure-callout>}}_{10}}{{\mathrm{\&theta;}}_1-{\mathrm{<figure-callout\; id="10"\; label="V"\; filenames="A9810052400111.png"\; state="\{\{state\}\}">V</figure-callout>}}_{10}}=\frac{{\mathrm{<figure-callout\; id="20"\; label="K"\; filenames="A9810052400111.png,A9810052400131.png"\; state="\{\{state\}\}">K</figure-callout>}}_{20}}{{\mathrm{\&theta;}}_2-V_{20}}----\left(12\right)$ And, (θ-V ₁₀) ²=(θ-V ₂₀) ²(13) all even ripples will be eliminated fully.Therefore, the present invention can reduce distortion, improves performance.

Compared with the prior art the present invention has some advantages, as reduces cost, and reduces direct current consumption, reduces noise, reduces because the problem that thermal stability is brought.

And the present invention compares with anti-series nonlinear compensation structure also some advantages.

The present invention has eliminated being connected of radio frequency (RF) and direct current, and has eliminated low-frequency disturbance.Second electric capacity 30 is with second bias source 18 and light source semiconductor diode 12 isolated coming, because electric capacity, resembles an open circuit for DC source.This has just reduced the contact of DC power supply and radio frequency source.This isolated low frequency interference that also helps to have reduced.The the first, the second and the 3rd inductance 22,24 and 26 has stoped low-frequency disturbance.

Inverse parallel non-linear compensation circuit of the present invention is compared with the anti-series structure, has reduced direct current consumption, has therefore also just reduced heating.The anti-series non-linear compensation circuit uses current offset, and makes the diode forward biasing, and this just needs a large amount of direct current consumptions.Working voltage biasing of the present invention, and with compensation semiconductor's diode 14 reverse bias.Back-biased diode is than the littler electric current of forward biased diode consumption.Littler electric current with compare identical or littler voltage with the anti-series structure, caused direct current consumption still less.Because direct current consumption is still less given birth to heat just still less among the present invention.Therefore, the present invention compares with the anti-series structure, has reduced thermal stability problems.

Use the inverse parallel structure also to reach lower noise level among the present invention.Forward biased anti-series compensates the variation of the big bias current of diode, has produced the unexistent noise of variation of the little bias current of reverse bias inverse parallel compensation diode.When relevant change was similar, the big electric current of forward bias anti-series had amplified the noise in the system.Moreover in the inverse parallel structure, the minimizing of RF/D.C. coupling is compared with the anti-series structure and has been reduced noise as mentioned above.

Inverse parallel structure among the present invention is compared with the anti-series structure, allows higher operating frequency.Reverse bias to compensation semiconductor's diode 14 is compared with forward bias, has enlarged its depletion layer.In the PN junction diode, a depletion layer that has enlarged means P district and N district far apart.This pole plate that is similar to plate condenser separates, and compares with the forward bias diode, and this effect has caused the minimizing of electric capacity (according to well-known formula C=(∈ * A)/d).The minimizing of electric capacity has improved the cut-off frequency of diode, because f _C=1/ (2 П C _OR _S), f wherein _CBe the cut-off frequency of diode, C _OBe the zero offset electric capacity of diode, R _SBe the interior resistance of diode 48.Reverse bias semiconductor diode 14 has reduced electric capacity, thereby has increased its cut-off frequency.This just allows this circuit, with in the anti-series structure, compensation semiconductor's diode 14 forward bias is compared, and is operated on the higher frequency (to reach 10GHZ).And, in ac equivalent circuit 50, light source semiconductor diode 12 and compensation semiconductor's diode 14 are replaced with semiconductor equivalent electric circuit 40 respectively, obtain a low equivalent inductance (inductance parallel connection), and anti-series will obtain a high inductance (inductance series connection).This lower inductance in the inverse parallel structure allows higher operating frequency.

The operating state that another improvement of the present invention is a light source semiconductor diode 12 does not change with the electric current in compensation semiconductor's diode 14.And in the anti-series of these diodes, the operating state of light source semiconductor diode 12 changes along with the change of the electric current in compensation semiconductor's diode 14.Isolated direct current biasing path can be when not influencing light source semiconductor diode 12, allows 12 bias current in compensation semiconductor's diode is regulated.

Under situation without departing from the spirit and scope of the present invention, several distortion of schematic diagram of the present invention shown in Figure 1 are possible.For example, first and second bias sources 16,18 can common ground (as shown in Figure 5).Compensation semiconductor's diode can have common earth terminal (as shown in Figure 6) with the one the second bias sources 16,18.Fig. 1 is compared with Fig. 6, and those skilled in the art can find out that the 3rd electric capacity 32 and first inductance 22 need not have been arranged among Fig. 6.

The present invention also can comprise other configuration.For example, can be with other semiconductor diodes of light source semiconductor diode 12, include, but are not limited to RF and microwave diode replaces.Also light source semiconductor diode 12 can be used photodetector, include, but are not limited to avalanche photodiode, field effect transistor or PIN diode and replace.In addition, compensation semiconductor's diode 14 can be used as signal sensor, and while light source semiconductor diode 12 is diode by way of compensation, to obtain the high linearity signal detection circuit.Fig. 7-9, respectively with Fig. 1,5,6 classes show such structure.It should be noted that the signal that is received by signal sensor has driven load 60, load 60 has replaced A.C. signal source 20 in shown signal sensor structure.

More than describe optimum embodiment of the present invention has been carried out abundant complete disclosing.Different distortion, the structure of replacement, and equivalent structure is very clearly for the personnel that correlation technique is arranged.Therefore, (protection) of the present invention scope is only limited by boundary in the appended claim.

Claims (17)

1. non-linear compensation circuit comprises:

One first semiconductor diode, it has the first voltage variable capacitance characteristic,

One second semiconductor diode, it and first semiconductor diode connect into the inverse parallel structure, this diode have the second voltage variable capacitance characteristic and

A DC power supply circuit, this circuit is connected with first and second semiconductor diodes, be respectively first and second semiconductor diodes first and second bias voltages are provided, like this, first and second bias voltages change the first and second voltage variable capacitance characteristics to reduce the harmonic distortion in first semiconductor diode.

2. device as claimed in claim 1, the second bias voltage reverse bias, second semiconductor diode.

3. device as claimed in claim 1, first semiconductor diode is made of a light source semiconductor diode, and this light source semiconductor diode is connected with the A.C. signal source.

4. as the device in the claim 1, also comprise an inductance and an electric capacity, they all are connected between the DC power supply in A.C. signal source and the DC power supply circuit, this inductance is used for stoping the A.C. signal of A.C. signal source to enter in the DC power supply in the DC power supply circuit, and this electric capacity is used for stoping the direct current in the DC power supply circuit to enter in the A.C. signal source.

5. device as claimed in claim 1, DC power supply circuit includes a DC power supply, this DC power supply has first end, second end and an earth terminal, first end links to each other with first semi-conductive first end, second end links to each other with second semi-conductive first end, and earth terminal links to each other with second semi-conductive second end with first semi-conductive second end.

6. install according to claim 1, DC power supply circuit includes first and second power supplys, and first power supply links to each other with first semiconductor diode, for it provides first bias voltage, second source links to each other with second semiconductor diode, for it provides second bias voltage.

7. as device as described in the claim 6, also include an electric capacity, it is connected between first and second semiconductor diodes.

8. device as claimed in claim 1, first semiconductor diode is made of a photodetector, and this photodetector is connected with a load.

9. device as claimed in claim 1, first semiconductor diode is made of a radio frequency (RF) diode.

10. in the device as claimed in claim 1, first semiconductor diode is made of a microwave diode.

11. device as claimed in claim 1 also comprises a variable resistor, the DC power supply in this resistance and the DC power supply circuit and second semiconductor are in series.

12. a low distortion photoelectric circuit that is used on the A.C. signal source, this photoelectric circuit comprises:

A light source semiconductor diode, it has the relevant capacitance characteristic of first voltage,

Compensation semiconductor's diode, it links to each other with the inverse parallel structure with the light source semiconductor diode, and in parallel with the A.C. signal source, this diode have the relevant capacitance characteristic of second voltage and

A DC power supply circuit, it is connected with the compensation semiconductor diode with the light source semiconductor diode, adds first and second bias voltages to light source semiconductor diode and compensation semiconductor's diode respectively.

13. device as claimed in claim 12, the light source diode is made of a laser diode.

14. device as claimed in claim 12, the light source diode is made of a light-emitting diode.

15. device as claimed in claim 12, straight power circuit reverse bias compensation semiconductor diode, forward bias light source semiconductor diode.

16. device as claimed in claim 12, the capacitance characteristic that first and second voltages are relevant is roughly close.

17. a high linearity optoelectronic semiconductor diode circuit that is used on the A.C. signal source, this circuit comprises:

A light source semiconductor diode, this diode have the first voltage variable capacitance characteristic,

Compensation semiconductor's diode, this diode and light source semiconductor diode and A.C. signal source connect into the inverse parallel structure, and this diode has the second voltage variable capacitance characteristic,

One first power supply, it is connected with the light source semiconductor diode, is used for adding forward bias voltage to the first light source semiconductor diode,

A second source, it is connected with the compensation semiconductor diode, is used for adding reverse bias voltage to compensation semiconductor's diode,

One first electric capacity, it is connected between first and second power supplys, is used for completely cutting off first and second power supplys,

One second electric capacity, it is connected between the A.C. signal source and first power supply, is used for stoping the direct current of first power supply to enter in the A.C. signal source,

One the 3rd electric capacity, it is connected between A.C. signal source and the second source, is used for stoping the straight electricity of second source to enter in the A.C. signal source,

A variable resistor, it and compensation semiconductor's diode and second source are in series, and like this, regulate variable resistor and adjust the second voltage variable capacitance characteristic, to reduce the harmonic distortion in the light source semiconductor diode.

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