[introduction]The likelihood in the design includes the sensor that needs ambipolar power supply or IC, or you need to make full use of converter of ambipolar input modulus (the dynamic limits of ADC) . Another reason that breaks up voltage course is, if you are in design of course of only power source,need intermediate course bias voltage.

The likelihood in the design includes the sensor that needs ambipolar power supply or IC, or you need to make full use of converter of ambipolar input modulus (the dynamic limits of ADC) . Another reason that breaks up voltage course is, if you are in design of course of only power source,need intermediate course bias voltage.

Term ” segregator of power source course ” described establish new 0-V reference point for circuit, the power source voltage that is VDD of course of only power source normally (the midpoint of VDD) is divided with 2. Total usable voltage keeps changeless, but you can regard its as the ± of ambipolar power source that distributings up and down in new 0-V reference VDD/2, this is called ” fictitious ground connection ” .

Found the orbit segregator of new fictitious ground contact to be able to be offerred or must absorb load current, and end must be outputted in its have capacitance to keep stable. A kind of method that makes fictitious ground connection is the operation amplifier that use configuration is unit gain bumper (Op Amp) .

The operation amplifier in orbit depart

The input voltage of operation amplifier bumper comes from resistor voltage divider, the half that setting of this voltage divider is power source voltage (VDD/2) . Voltage divider and C3 are detached, in order to stabilize voltage, the noise that prevents VDD to go up or ripple (graph 1) . Add R3 to be able to be restricted flow into operation amplifier to be not what cite a base instead any electric current. Rise when VDD or drop and when C1, C2 and C3 capacitor charge or discharging, this electric current can flow.

Graph the means of amplifier of use operation of segregator of 1 voltage course. Origin: Heart state apparatus

Accordingly, the output of operation amplifier is Vsplit = VDD/2. The output of bumper should use capacitance to go Ou, power source course is this kind of circumstance normally. But, although most operation amplifier has the output load capacitance of law of a few skins to also can become not stable, need additional technical talent to make its stable.

Accordingly, choose to have the amplifier of operation of inherently stable sex that outputs laden capacitance indefinitely please. Design research to this, we use OPA994, it can detect automatically the laden capacitance on its output optimizes his in-house compensation outputs capacitance greatly with allowing to use. It still can be being offerred or absorb VDD/2 output holds while tens of milliampere are laden, if data is expressed,different VDD is worth place to show in the curve.

Considering the bad influence of temperature and change of power source voltage, and equipment is to pull electric current to still suck electric current, pull electric current or the safe cost that absorb electric current to be ± 30 MA. Can use the data that answers relatively with application to express a curve to increase electric current of this ± 30 MA.

We emulate the imitate in software in TINA-TI OPA994 orbit alloter, output frequency in order to check its to answer stability. Graph the response that 2 medium baud graphs showed stability, phasic below the alternate frequency of 16.65 KHz abundant is spent it is 66.7 degrees. Should answer to come true, OPA994 reduces its bandwidth automatically 16.65 KHz from 18 MHz.

Graph the baud graph of 2 OPA994 emulates the output that showed its are inputted instead. Origin: Heart state apparatus

We are right graph 1 undertook time domain is emulated, among them we change laden twinkling apply at output (graph 3) . This involves switch to join the resistor of 120 Ω between Vsplit and primitive 0 V is laden. We bring to bear on when T = 2 Ms laden, move when T = 6 Ms except it. Join the load of resistor of Ω of the 2nd 120 between VDD and Vsplit is when T = 4 Ms switch, move when T = 8 Ms except. Load of 120 Ω is 2.5 V, load current of transient state of 21 MA of ≈ of 120 Ω .

Graph 3 emulate showed laden twinkling changes how to apply at output. Origin: Heart state apparatus

Simulative purpose is to examine the voltage deviation of Vsplit to check stability, this expresses by the response with good damp. In great majority application, laden twinkling becomes can small much, what accordingly this imitate shows is bad situation. If what you see, answer damp good. To 21 MA load rank is jumped (source or receiver) , output deviation is 9 MV, restore time to be 0.37 millisecond.

Referenced operation amplifier

In applying actually, power supply load can be catenary of operation amplifier signal normally. In the graph 4 shown TINA-TI are emulated in, OPA171 operation amplifier consults the Vsplit fictitious ground connection of OPA994 is outputted. Configuration of OPA171 operation amplifier is for gain – of 100 turn over photograph amplifier. The voltage of OPA171 is inputted (V IN) is wave of sine of peak value of ± 20 MV, referenced also Vsplit.

 Graph 4 on the graph showed OPA994 divides course and OPA171 to turn over photograph amplifier to emulate. Origin: Heart state apparatus

Graph the emulation output of 5 shows, OPA994 (ILOAD) provides a few electricity only (A) of μ of ± 20, negligible to the interference of Vsplit course not plan. The static electric current of OPA171 comes from VDD to 0 V, the voltaic origin of OPA994 separate course or absorb come from Vsplit to reference is inputted and output signal.

 Graph 5 emulation output show OPA994 provides a few electricity only, negligible to the interference of Vsplit course not plan. Origin: Heart state apparatus

OPA171 outputs the 2 V that it is ± , as a result of the input of operation amplifier maladjusted voltage is multiplied with its noise gain (namely gain is 101) , because this is put in extra output voltage weight. Of OPA171 in all the model is restrained than but the interference on abate Vsplit or maladjusted.

We tested the circuit that the graph shows 1 times, go to the switch load of 120 Ω from Vsplit switch primitive 0 V, answer in order to check laden transient state. Graph 6 showed communication coupling Vsplit is outputted, gave out deviation of peak value of 4 MV peak, reflected imitate result.

Graph load of Ω of indication 120 of 6 tests result puts through and disconnect. Origin: Heart state apparatus

Next we used input of wave of sine of ± 20 MV, 1 KHz to test the circuit that the graph shows 4 times. Graph 7 medium tests show as a result, output is ± 2 V (the photograph is fictitious to Vsplit the ground) , add deflection (the input deflection voltage that gives operation amplifier) .

 Graph 7 on the graph showed OPA171 is outputted (– of G = 100) , the input is ± 20 MV. Origin: Heart state apparatus

Like all operation amplifier, vsplit outputs maladjusted voltage to be able to change along with load current. Graph 1 showed this imitate result, and graph 8 showed ± 40 MA is laden the 14 MV deviation inside the result inside limits and this load limits.

Graph the circumstance that 8 indication load current change along with Vsplit. Origin: Heart state apparatus

The maladjusted voltage of the amplifier of operation of ascribe of 3 MV maladjusted voltage when 0 MA, the input in adding R1, R2 and R3 resistance slants the maladjusted voltage of buy electric current. One increases to be equal to voltage divider resistor in the feedback method of operation amplifier (R1//R2) and Ω of R3 (6 K) the resistor of shunt-wound combination, can eliminate slant the maladjusted tension that buy electric current causes.

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