CN101060310A - A DC level switching circuit - Google Patents

Abstract

The disclosed dc electric level conversion circuit comprises: an OA with its in-phase end connecting the input signal and at least one resistant device to the output end, and a reference voltage source connecting at least one resistant device with the inverse-phase end of OA. This invention holds the advantages of low cost, and can converse dc offset level even the input signal has no any drive capacity.

Description

A kind of DC level switching circuit

Technical field

The present invention relates to DC level switching circuit, relate in particular to a kind of DC level switching circuit that is applied in the integrated circuit.

Background technology

Along with the development of semiconductor technology, it is more and more lower that the power supply of integrated circuit also becomes, and a lot of circuit adopt lower working power in order to reduce power consumption.But some chip but can not be operated under the low power supply, so data just need level shifting circuit in the transmission of these chip chambers.And, along with the development of SOC (SOC (system on a chip)) technology in recent years, on chip piece, many cover power supplys are usually arranged, therefore, different DC level is arranged in disparate modules, and how transmitting the signal of these different DC level and don't introducing noise becomes the problem that troubles the circuit design engineer.The level conversion of analog signal then becomes a difficult point.

DC level switching circuit is divided digital level conversion and analog level conversion.The digital level conversion refers to that logic level converts another kind of current potential to from a kind of current potential, and shown in Figure 1 is the example that a digital low level changes into high level.As can be seen from Figure 1 the level conversion of digital circuit is the conversion of representing under the different situations between the current potential of logical one.The example of another digital level conversion is shown in Fig. 2 a, Fig. 2 b, and Fig. 2 a is the high low transition circuit that changes, and this circuit has adopted a phase inverter that logic high " 3.3V " is changed into logic low " 1.2V ".Fig. 2 (b) is one logic low " 1.2V " is changed into the circuit of high level " 3.3V " that this circuit has utilized two PMOS pipes to form one and latched structure, forms positive feedback, thereby has accelerated the reaction of circuit.

The level conversion of analog circuit requires the direct current composition of analog signal is carried out lifting or reduction, and Alternating Component amplifies or decays, and reduces the distortion of signal simultaneously to greatest extent.From schematic diagram 3 as can be seen, the analog level conversion mainly is the direct current composition that changes analog signal according to designer's needs.Figure 4 shows that and adopt capacitance to carry out DC level switching circuit, circuit adopts the capacitance of a microfarad magnitude, through the signal after directly, becomes V in the reverse input end DC level of amplifier _CMSuppose that input signal is a sine wave in Fig. 4, its input DC biased level is V ₀, it is Δ V that amplitude changes, then input signal can simply be expressed as V _IN=V ₀+ Δ V (frequency of having ignored signal here), so through capacitance and utilize the short and homophase amplification principle of void of amplifier, output signal can be expressed as:

$V_{\mathrm{OUT}}=V_{\mathrm{CM}}+(1+\frac{R1}{R2}\mathrm{\ΔV})---\left(1\right)$

First initial as can be seen DC biased level V from (1) formula the right ₀Changed into V _CMAdopt this method, can easily any input dc power be flatted turn turns to the level that needs, but this method has tangible limitation.One, it needs a bigger capacitance, and signal is by after straight, and THD (total harmonic distortion) is also with variation.Its two, be if this circuit is in the SOC (system on a chip) (SOC), certainly will increase by two PIN pin and connect this big electric capacity because like this electric capacity can't be integrated in integrated circuit, so only take plug-in mode, this certainly will increase cost.

The another kind of benchmark dividing potential drop that adopts is carried out the tributary level shifting circuit as shown in Figure 5.This circuit adopts resistance R 1 and R2 to reference voltage V _FEFDividing potential drop, with the flat level that needs that is transformed into of input dc power, it has avoided the use capacitance, has reduced system cost.Suppose that Fig. 5 input signal is a sine wave, its input DC biased level is " 0V " (it is the signal of " 0V " that this connected mode of this circuit can only be changed the input biasing), and it is Δ V that amplitude changes, and then input signal can simply be expressed as V _IN=Δ V (frequency of having ignored signal here).By reference voltage is carried out dividing potential drop, produce a direct current biasing at the positive input of amplifier, be reflected in output end signal and be:

$V_{\mathrm{OUT}}=\frac{R2}{R1}{V}_{\mathrm{REF}}+\frac{R4}{R3}\mathrm{\ΔV}---\left(2\right)$

Can find out, can change DC biased level for first from (2) formula the right by the value of adjusting VREF or resistance R 1, R2.But this scheme is owing to there is a path between signal and ground, so require input signal that certain driving force is arranged.

Summary of the invention

Technical problem to be solved by this invention is: a kind of new DC level switching circuit is provided, and this circuit can solve prior art benchmark dividing potential drop method and require input signal to have the problem of certain driving force.

Technical scheme of the present invention is:

A kind of DC level switching circuit comprises an operational amplifier, a reference voltage source, and the in-phase input end of described operational amplifier connects input signal; Be connected at least one resistive components and parts between the output of described operational amplifier and the inverting input; Be connected at least one resistive components and parts between the inverting input of described operational amplifier and the described reference voltage source.

Described DC level switching circuit, wherein: the resistive components and parts that are connected between the output of described operational amplifier and the inverting input are second resistance, the resistive components and parts that are connected between the inverting input of described operational amplifier and the described reference voltage source are first resistance, and the ratio of described second resistance and first resistance is determined by the gain of operational amplifier.

Beneficial effect of the present invention is: DC level switching circuit of the present invention, both inherited the low-cost advantage of benchmark dividing potential drop method, and because input signal directly is added in the in-phase input end of operational amplifier, avoided the path between signal and the ground, solved the problem that requires input signal to have driving force, even input signal without any driving force, also can be finished the conversion of the DC biased level of analog signal.

Description of drawings

Fig. 1 is a digital DC level conversion schematic diagram;

Fig. 2 a is the high low transition circuit that changes of numeral;

Fig. 2 b is the low high level change-over circuit that changes of numeral;

Fig. 3 is an analog signal level transfer principle schematic diagram;

Fig. 4 realizes DC level switching circuit for utilizing capacitance;

Fig. 5 utilizes the benchmark dividing potential drop for prior art and realizes DC level switching circuit;

Fig. 6 realizes DC level switching circuit for the present invention.

Embodiment

With embodiment the present invention is described in further detail with reference to the accompanying drawings below:

DC level switching circuit of the present invention as shown in Figure 6.Comprise an operational amplifier, a reference voltage V _REF, between the output and inverting input of amplifier, and amplifier's inverting input and described reference voltage V _REFBetween respectively be provided with an alternating current-direct current signal path, as shown in Figure 6, at amplifier's inverting input and V _REFBetween connect a resistance R 1, be connected a resistance R 2 between the output of amplifier and the inverting input.Signal directly is added in the in-phase input end of amplifier, has avoided the path between signal and the ground, so require input signal any driving force is not arranged, and therefore is fit to the level shift of weak signal.This circuit is by adjusting V _REFThe size of value can promote or be reduced to the level that the designer requires with the DC level of exporting analog signal easily.

Introduce operation principle of the present invention below.Suppose that input signal is a sine wave signal in Fig. 6, its input DC biased level is V ₀, the amplitude variable quantity is Δ V, then input signal can simply be expressed as V _IN=V ₀+ Δ V (frequency of having ignored signal here).(the empty short voltage difference of two inputs of integrated transporting discharging that is meant is in close proximity to zero usually to utilize the short notion of void of amplifier, but not short circuit, so be called for short " empty short "), equal the DC biased level V of in-phase input end (node is 2.) so in the DC biased level of the inverting input (node is 1.) of amplifier ₀Simultaneously because in output and reference voltage V _REFBetween have a DC channel, can stablize the DC biased level of output.Output and reference voltage V _REFBetween the electric current of DC channel can be expressed from the next:

$I=\frac{V_0-{\mathrm{<figure-callout\; id="1"\; label="V\; REF\; R"\; filenames="A20061006037800081.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{REF}}}{R_{}}$

Know resistance R by Ohm's law ₂The voltage drop V at two ends _R2For

V _R2＝I·R ₂

So direct current biasing of output

$V_0^{\&prime;}={\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="A20061006037800082.png,A20061006037800083.png"\; state="\{\{state\}\}">V</figure-callout>}}_0+V_{R2}={\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="A20061006037800082.png,A20061006037800083.png"\; state="\{\{state\}\}">V</figure-callout>}}_0+\frac{(V_0-V_{\mathrm{REF}})R_2}{R1}---\left(3\right)$

Amplification according to in-phase amplifier concerns the alternating component of output signal as can be known

$\mathrm{\&Delta;}{V}^{\&prime;}=1+\frac{R2}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A20061006037800081.png"\; state="\{\{state\}\}">R</figure-callout>}1}\mathrm{\&Delta;V}---\left(4\right)$

Wherein Δ V represents the alternating component of input signal.

So complete output signal expression formula is

V _OUT＝V′+ΔV′ (5)

With (3) formula and (4) formula substitution (5) formula, finally obtain the output expression formula of finishing (6).

Can find out that by second on (6) formula the right the ratio of adjusting R1 and R2 can change Amplifier Gain, and can find out that the ratio of R1 and R2 also can change the output DC biased level from first, if but the value of R1 and R2 determined, adjust V so _REFValue can change the output DC biased level.Therefore circuit of the present invention can be adjusted amplifier gain by the ratio of R1 and R2, and by adjusting V _REFThe size of value, the DC level that to export analog signal easily promotes or is reduced to the level that the designer requires, and because signal directly is added in the in-phase input end of amplifier, even if input signal without any driving force, also can be finished the conversion of the DC biased level of analog signal.This circuit is specially adapted to the integrated circuit (IC) system of many cover power supplys.

Should be understood that; DC level switching circuit of the present invention; above-mentioned description at preferred embodiment is too concrete; can not therefore be interpreted as restriction to scope of patent protection of the present utility model; for those of ordinary skills; can be equal to replacement or change according to technical scheme of the present invention and inventive concept thereof, for example adopt variable resistor substitutional resistance R1 and R2, and all these changes or replacement all should be belonged to the protection range of the appended claim of the present invention.

Claims (2)

1, a kind of DC level switching circuit comprises an operational amplifier, and a reference voltage source is characterized in that: the in-phase input end of described operational amplifier connects input signal; Be connected at least one resistive components and parts between the output of described operational amplifier and the inverting input of operational amplifier; Be connected at least one resistive components and parts between the inverting input of described operational amplifier and the described reference voltage source.

2, DC level switching circuit according to claim 1, it is characterized in that: the resistive components and parts that are connected between the output of described operational amplifier and the operational amplifier inverting input are second resistance, the resistive components and parts that are connected between the inverting input of described operational amplifier and the described reference voltage source are first resistance, and the ratio of described second resistance and first resistance is determined by the gain of operational amplifier.

Images