CN100511078C - Load level switching circuit - Google Patents

Abstract

The present invention discloses a load-level conversion circuit which comprises a positive-level voltage setting unit, an error control unit, a feedback circuit and a current-voltage conversion unit; the positive-level voltage setting unit can be used for leading in positive voltage level; the error control unit can be used for controlling the controllable current source according to the voltage-level generating signal from the feedback circuit and the positive-level voltage setting unit; the feedback circuit can be used for feeding the controllable current source back to the error control unit; based on the error control unit, the controllable current source can generate current; the current-voltage conversion unit can convert the current generated by the controllable current source into the negative output-voltage level, and output the negative output-voltage level; through the present invention, the output negative level can be stabilized by the circuit, namely, if the negative current occurs to bias for some reasons, the negative level is stable relevant to the benchmark of the negative current; in addition, the negative level is not sensitive to the changes of the temperature, and the adjusting range of the negative level can be set according to the requirement.

Description

Load level switching circuit

Technical field

The present invention relates to apply to the analog input amount control field of optical module high speed driver, relate to load level switching circuit particularly.

Background technology

In the DWDM optical transmission system, optical module is transmission and a receiving-member the most basic in the system.Wherein, the quality of the light eye pattern that optical transmission module sends and the performance of whole transmission system are closely related, in case after the index of eye pattern is adjusted to and meets the requirements, generally just can not be subjected to the influence of extraneous factor and change, extraneous factor is temperature, supply voltage etc. normally.In order to guarantee that light sends out the stability of the light eye pattern of module, just must guarantee that light sends out the high-speed driver working stability in the module.

The use of the high-speed driver in the existing optical transmission module as shown in Figure 1.They substantially all are the negative supply power supplies.Also have some adjustable negative level controlled quentity controlled variables such as VON level, V simultaneously _MODVoltage, point of crossing regulation voltage wait the duty of controlling and driving chip.The high-speed driver chip MAX3941, VSC7984, the VSC7937 etc. that use now are to utilize such control model.

Because V _ONLevel, V _MODVoltage, point of crossing regulation voltage are negative levels, but general control signal is the positive level that the dividing potential drop on digital regulation resistance produces by the D/A output of MCU or a positive voltage reference, this controls high-speed driver with regard to needing a level shifting circuit to convert positive level to negative level, as shown in Figure 2.

In order to guarantee the steady operation of high-speed driver in some working points to this transmission system the best, this level shifting circuit need satisfy following requirement: this negative level wants linear in the control positive level; This negative level is not subjected to negative supply to draw inclined to one side influence, and is stable with respect to negative supply; This negative level does not change with ambient temperature.

For these reasons, need a kind of adjustable load level switching circuit.

Summary of the invention

Fundamental purpose of the present invention is to provide a kind of negative level stable and linear in the load level switching circuit of controlling positive level and not changing with ambient temperature with respect to negative supply.

According to an aspect of the present invention, this load level switching circuit comprises: positive level setting voltage unit is used to introduce positive voltage level; Error control unit is used for producing control signal according to the voltage level that comes self-feedback ciucuit unit and positive level setting voltage unit and controls controllable current source; The feedback circuit unit is used for the voltage level of controllable current source is fed back to error control unit; Controllable current source based on the control of error control unit, produces electric current; And the current/voltage converting unit, the current conversion that controllable current source is produced is a negative output voltage level and with its output.

In this load level switching circuit, also comprise: negative reference power supply is used for to load level conversion single service; And output unit, be used to export the voltage difference between the voltage that negative output voltage level and negative reference power supply provide.

In this load level switching circuit, error control unit, feedback circuit unit and controllable current source form a loop.The positive voltage level that positive level setting voltage unit produces is the adjustable positive voltage level of scope, and the negative output voltage level is the adjustable negative output voltage level of scope.Positive level setting voltage unit comprises a variohm, and wherein, the output terminal of variohm is the output terminal of positive level setting voltage unit.

In addition, in this load level switching circuit, controllable current source is a triode, and triode comprises: base stage is connected to the output terminal of error control unit; Emitter is connected to the input end of feedback circuit unit; And collector, be connected to the current/voltage converting unit.Wherein, triode is the positive-negative-positive triode.

In addition, in this load level switching circuit, error control unit comprises an operational amplifier, and operational amplifier comprises: in-phase input end is connected to the output terminal of positive level setting voltage unit; Inverting input is connected to the output terminal of feedback circuit unit; And output terminal, be connected to the input end of controllable current source by resistor.

By above-mentioned aspect of the present invention, the negative level range of adjustment of this circuit output can be set as requested.The negative level that this level shifting circuit produces is stable with respect to negative supply, does not vary with temperature and changes.

Other features and advantages of the present invention will be set forth in the following description, and, partly from instructions, become apparent, perhaps understand by implementing the present invention.Purpose of the present invention and other advantages can realize and obtain by specifically noted structure in the instructions of being write, claims and accompanying drawing.

Description of drawings

Accompanying drawing is used to provide further understanding of the present invention, and constitutes the part of instructions, is used from explanation the present invention with embodiments of the invention one, is not construed as limiting the invention.In the accompanying drawings:

Fig. 1 shows the synoptic diagram of the position of negative level change-over circuit in the high-speed driver control circuit of prior art;

Fig. 2 shows the synoptic diagram of the function of load level switching circuit;

Fig. 3 shows the block diagram according to the load level switching circuit of the embodiment of the invention;

Fig. 4 shows the curve map according to the setting range of the controlled quentity controlled variable of the embodiment of the invention;

Fig. 5 shows the structural drawing according to the load level switching circuit of the embodiment of the invention.

Embodiment

Below in conjunction with accompanying drawing the preferred embodiments of the present invention are described, should be appreciated that preferred embodiment described herein only is used for description and interpretation the present invention, and be not used in qualification the present invention.

In an embodiment of the present invention, provide a kind of load level switching circuit.

Fig. 3 shows the block diagram according to the load level switching circuit of the embodiment of the invention.As shown in Figure 3, it comprises: positive level setting voltage unit 1, error control unit 2, feedback circuit unit 3, controllable current source unit 4, current/voltage converting unit 5, negative supply reference cell 6.Wherein, negative supply reference cell 6 is negative level reference voltages; Positive level setting voltage unit 1 is a positive voltage that scope is adjustable, and this range of adjustment has determined the range of adjustment of last output negative level; Error control unit 2 links are as controller controllable current source unit 4 of difference generation controlled quentity controlled variable control according to feedback circuit unit 3 and positive level setting voltage unit 1; Current/voltage converting unit 5 converts the electric current of controllable current source unit 4 outputs to last negative level through current/voltage converting unit 5.

This scheme is insensitive to temperature.Even negative supply reference cell 6 is temperature variant in the scheme, can passes through control loop that error control unit 2, feedback circuit unit 3, controllable current source unit 4, current/voltage converting unit 5 form and produce the output negative level constant with respect to negative supply reference cell 6.

Be to utilize this negative level change-over circuit to produce the concrete application of adjustable negative level signal controlling EML driver VSC7984 below.Fig. 5 shows the structural drawing according to the load level switching circuit of the embodiment of the invention.As shown in Figure 5, wherein, Rr, stabilivolt, R4 are power supply, the R1 in this circuit, R _v, R2 formed the level setting voltage unit 1 among Fig. 3; Operational amplifier has been formed the error control unit 2 among Fig. 3; C1, R3, R5 have formed the feedback circuit unit 3 among Fig. 3; Q1 has formed the controllable current source unit 4 among Fig. 3; R6 has formed current/voltage converting unit 5 among Fig. 3;-5.0V supply voltage promptly is a negative supply reference cell 6 among Fig. 3.

According to the databook of VSC7984, three controlled quentity controlled variable V are arranged _PW, V _MOD, V _OFSNeed control, Fig. 4 shows the curve map according to the setting range of the controlled quentity controlled variable of the embodiment of the invention.As shown in Figure 4, the control corresponding scope obtains following relational expression, wherein V _EENegative supply power supply-5.0V for VSC7984.

V _EE+0.5V≤V _PW≤V _EE+2.5V (1)

V _EE≤V _MOD≤V _EE+2.0V (2)

V _EE≤V _OFS≤V _EE+2.0V (3)

Utilize the negative level change-over circuit shown in Figure 5 can be respectively to V _PW, V _MOD, V _OFSControl.The range of adjustment that provides according to equation (1), (2), (3) can be determined the parameter in three picture groups 5.

From temperature characterisitic, thermally sensitive device is PNP triode Q1 in the circuit of Fig. 5, and the thinking of design is to eliminate because the temperature characterisitic of PNP influences the work of circuit by the mode of feedback.Assumed temperature increases, and the beta coefficient of Q1 increases, and corresponding i increases, and the emitter voltage of Q1 descends, and the negative input end voltage of amplifier descends, and causes the emitter voltage of Q1 to rise, | V _BE| reduce, i reduces.Make negative level to temperature-insensitive by feedback circuit.

Analyzed by to V at this _PWControl determine each parameter among Fig. 5: the detailed process of R1～R5 and C1.

Because the minimum 0V that is not less than of Q1 base stage level can obtain:

V _r-iR ₅-V _{BE (Q1)}〉=0 (base current of ignoring Q1)

$i=\frac{V_{\mathrm{PW}}-{\mathrm{<figure-callout\; id="6"\; label="V\; EE\; R"\; filenames="C200710127677E00121.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{EE}}}{R_{}}\&DoubleRightArrow;i_{\max }=\frac{2.5\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="C200710127677E00121.png"\; state="\{\{state\}\}">V</figure-callout>}}{1\mathrm{K\&Omega;}}=2.5\mathrm{mA}$

Usually, V _{BE (Q1)}=0.9V

${\mathrm{<figure-callout\; id="5"\; label="R"\; filenames="C200710127677E00121.png"\; state="\{\{state\}\}">R</figure-callout>}}_5<\frac{2.5V-V_{\mathrm{BE}\left(Q1\right)}}{2.5\mathrm{mA}}=\frac{2.5V-0.9V}{2.5\mathrm{mA}}=640\mathrm{\&Omega;}$

Get R5=511 ohm.

Utilize reference voltage V _rWith digital regulation resistance R _vProduce setting voltage V _a, V wherein _rAnd V _aRelation shown in equation (1):

$V_a=\frac{(1-\mathrm{\&alpha;})R_V}{R_V+R_2}{V}_r---\left(4\right)$

Can also obtain simultaneously:

$i=\frac{V_r-V_a}{{\mathrm{<figure-callout\; id="5"\; label="R"\; filenames="C200710127677E00121.png"\; state="\{\{state\}\}">R</figure-callout>}}_5}=\frac{V_r}{R_5}[1-\frac{(1-\mathrm{\&alpha;})R_V+R_2}{R_V+{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="C200710127677E00121.png"\; state="\{\{state\}\}">R</figure-callout>}}_1+R_2}]=\frac{V_r}{R_5}\left[\frac{\mathrm{\&alpha;}{R}_V+R_1}{R_V+{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="C200710127677E00121.png"\; state="\{\{state\}\}">R</figure-callout>}}_1+R_2}\right]---\left(5\right)$

$V_G={\mathrm{<figure-callout\; id="6"\; label="iR"\; filenames="C200710127677E00121.png"\; state="\{\{state\}\}">iR</figure-callout>}}_6+V_{\mathrm{EE}}=\frac{R_6}{R_5}\left[\frac{\mathrm{\&alpha;}{R}_V+R_1}{R_V+R_1+R_2}\right]V_r+V_{\mathrm{EE}}---\left(6\right)$

Can obtain negative level V according to equation (4), (5), (6) _GSExpression formula (7).This negative level V as can be seen from equation (1) _GSIt doesn't matter with the negative supply benchmark; If variohm α R _vIncrease or reduce negative level V _GSWill reduce accordingly or increase, promptly change setting voltage and can change negative level voltage by variohm.

$V_{\mathrm{GS}}=V_G-V_{\mathrm{EE}}=\frac{R_6}{R_5}\left[\frac{\mathrm{\&alpha;}{R}_V+R_1}{R_V+R_1+R_2}\right]V_r---\left(7\right)$

Obtain at V according to equation (1), (7) _PWThe border equation of range of adjustment.

$0.5V=\frac{1\mathrm{K\&Omega;}}{511\mathrm{\&Omega;}}\left[\frac{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="C200710127677E00121.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}{50\mathrm{K\&Omega;}+{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="C200710127677E00121.png"\; state="\{\{state\}\}">R</figure-callout>}}_1+R_2}\right]2.5V$

$2.5V=\frac{1\mathrm{K\&Omega;}}{511\mathrm{\&Omega;}}\left[\frac{50\mathrm{K\&Omega;}+{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="C200710127677E00121.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}{50\mathrm{K\&Omega;}+R_1+R_2}\right]2.5V$

Can be in the hope of R1=22.1K, R2=100K.In addition, the value of R3, R4, C1 is inessential, can get R3=12.1K, R4=511, C1=0.1uF.

Profit uses the same method, and can obtain V according to equation (2), (3), (7) _MOD, V _OFSThe parameter of two groups of R1～R5 and C1.

In sum,, utilize this circuit can make the negative level of output stable, that is to say that this negative level is stable with respect to the negative supply benchmark if negative supply produces for some reason to be drawn partially according to the present invention.This negative level is insensitive to temperature variation simultaneously, and the negative level range of adjustment can be set as requested.

The above is the preferred embodiments of the present invention only, is not limited to the present invention, and for a person skilled in the art, the present invention can have various changes and variation.Within the spirit and principles in the present invention all, any modification of being done, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (7)

1. a load level switching circuit is characterized in that, comprising:

Positive level setting voltage unit is used to introduce positive voltage level;

Error control unit is used for producing control signal according to the voltage level that comes self-feedback ciucuit unit and described positive level setting voltage unit and controls controllable current source;

Described feedback circuit unit is used for the voltage level of described controllable current source is fed back to described error control unit;

Described controllable current source based on the control of described error control unit, produces electric current;

Current/voltage converting unit, the current conversion that described controllable current source is produced are negative output voltage level and with its output;

Negative reference power supply is used for to described load level switching circuit power supply; And

Output unit is used to export the voltage difference between the voltage that described negative output voltage level and described negative reference power supply provide,

Wherein, the positive voltage level of described positive level setting voltage unit generation is the adjustable positive voltage level of scope.

2. load level switching circuit according to claim 1 is characterized in that, described error control unit, described feedback circuit unit and described controllable current source form a loop.

3. load level switching circuit according to claim 1 is characterized in that, described negative output voltage level is the adjustable negative output voltage level of scope.

4. load level switching circuit according to claim 1 is characterized in that, described positive level setting voltage unit comprises a variohm, and wherein, the output terminal of described variohm is the output terminal of described positive level setting voltage unit.

5. load level switching circuit according to claim 1 is characterized in that, described controllable current source is a triode, and described triode comprises:

Base stage is connected to the output terminal of described error control unit;

Emitter is connected to the input end of described feedback circuit unit; And

Collector is connected to described current/voltage converting unit.

6. load level switching circuit according to claim 5 is characterized in that, described triode is the positive-negative-positive triode.

7. load level switching circuit according to claim 4 is characterized in that, described error control unit comprises an operational amplifier, and described operational amplifier comprises:

In-phase input end is connected to the described output terminal of described positive level setting voltage unit;

Inverting input is connected to the output terminal of described feedback circuit unit; And

Output terminal is connected to the input end of described controllable current source by resistor.

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