TI高精度实验室-噪声 3.pdf.pdfTI高精度实验室-噪声 3.pdfpdf,TI高精度实验室

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详细说明：TI高精度实验室-噪声 3.pdfpdf,TI高精度实验室-噪声 3.pdf●在开始手工计算前,我们先一起关注下不同类型运放的电流和电压噪声指标。我们知道电压噪声与该运放的静态电流相关性非常大。他们二者之间是成反比的,也就是说高静态电流的运放一般都具有比较低的电压噪声。举例来说,我们来对比下OPA349和OPA3,你就会发现高静态电流确实伴随着低电压噪声指标。同时,我们也发现,同样静态电流下, Bipolar结构的运放电压噪声往往都比CMOS结构的要低一些。例如,从CMOS结构的 OPA350和 biploar结构的OPA21l对比看可以发现这个规律。这甲值得注意的是,即使CMOS运放的静态电流高一些时, Bipolar运放仍然具有更低些的电压噪声性能 ●对于电流噪声,则和电压噪声有所不同,它与静态电流无关。CMOS运放的电流噪声般都比 Bipolar的要低。一般来说,你会发现 bias current(偏置电流)比较低的运放总是具有较低的电流噪声。从这个表格中我们可以看到不同运放的噪声水平。换句话说,大多数运放的电压噪声都在1个或几个 nV/rHz到几百 n/rthz之间,而电流噪声则在1个或者小于1个fA/rtHz到几千 fa/rthz之间。 Example Noise Calculation Given: R2 1k OPA62 R1+OCk Noise gain°f101 V115 Find(RtI, Rto) Voltage noise Current noise U1//BB Resistor noise VG1 ≡V215 中 TEXAS INSTRUMENTS o In this calculation, we will examine an OPA627 in a non-inverting configuration with a gain of 101 v/. the total noise at the output will be the sum of op-amp voltage noise, op-amp current noise, and resistor noise. We will consider both the 1/f region and the broadband region in the spectral density curve We will also have to consider the noise bandwidth and the noise gain of the circuit ●在这个估算示例中,OPA627同相放大电路的增益是10lVV。其输出总噪声应该是电压噪声,电流噪声和电阻噪声的总和。我们将考虑噪声频谱密度曲线中的l/区域和宽带区域。同时我们还需要考虑该电路的噪卢带宽和噪声增益 Example Noise Calculation INPUT VOL TAGE NOISE SPECTRAL DENSITY OPEN-LOOP GAIN VS FREQUENCY 口 HHHH日 50nV/HZ ■■■ 5nV/VHz 0 |■□ 10k100k1M10M100M Frequency (Hz) Frequency(Hz) Unity Gain Bandwidth =1 6MHZ Closed Loop Bandwidth =16MHZ /101= 158kHZ TEXAS INSTRUMENTS o the left hand curve is the voltage spectral density curve. Remember from earlier videos that it has a 1/f and broadband region the right hand curve is the open loop gain(aol curve. the bandwidth of the our circuit is determined by the aol curve because there is no other filter. dividing the opA627 s unity gain bandwidth of 16MHz by our gain of 101, we get a closed-loop bandwidth of 158kHz. this can also be seen graphically 大家看到左手边是电压噪声频谱密度曲线。回想一下我们早前学习过的视频,该曲线包括Lf区域和宽带区域。而右边的曲线则是其开环增益频响曲线。因为范例电路中没有其他的滤波器,所以此电路的带宽主要是由开环增益曲线米确定的。 ●我们将OPA627的单位增益带宽,这里为16MHz,除以电路噪声增益101 VV,我们得到闭环带宽为158KHz。同样我们也可以从右图中看岀这个值。 Example voltage Noise calculation Broadband Noise Component BWn=(K1)x(1)=(1.7)(158kH2)=248kH Fnsg=PpL RW=( nv/v2)*(248KI1 )=2490mV ms 1/f voltage Noise Component Pomm=ertVe=(50 nV/zv(11l)=50nV -4()-面(的- Total Noise Referred to the Input of the amplifier: E:=(59+(m=290mWm90920=2y 中 TEXAS INSTRUMENTS o Now that we have learned all the equations for the op-amp voltage noise in the previous videos let's compute it for this example. Inspection of the results shows that the 1/f noise component of 192nV is not significant in this example compared to the broadband noise of 2490nv. this is fairly typical of wide bandwidth examples. Also note that the results are added using root sum of squares, for a total input-referred noise of 2497nV ●由于我们在之前的视频中已经掌握了所有运放电压噪声的计算公式,现在就起来计算这个例子的噪声。我们可以看到f噪声是192nV,相较于宽带噪声2490nV,它并不是占主要部分。这是一个相当典型的以宽带噪声为主的例子。同时我们注意到,这两个部分的噪声需要采用平方和再开方来计算, 我们得到总的输入相关噪声为2497nV EXample Current Noise Calculation PARAN ETEN CPA517BM. B2 5M UNT NOISE put Vot age Nose Nise Emily: IE 1DMZ 820m/z Note: This example amp doesnt have 1/f component for current noise Collage NUise, EW=0.1iiLu1Dh 0.6 L5 ppp Input D as Currert N)se Mose DeNt↑-1 25,正 Current noise ew=D1-itolH 305益,压 ()KR) VF1 CReg=R1 I Ri 中 TEXAS INSTRUMENTS 6 Now that we have the op-amp voltage noise component, let's compute the effect of current noise. For a non-inverting amplifier, the current noise flows through the parallel combination of R1 Rf. This relationship can be derived using the same op amp analysis techniques that would be used for a dc current source. The current noise is multiplied by the equivalent resistance to generate an input referred noise voltage. Let's look at the numbers for this example ●现在我们已经得到了电压噪声部分,接下来计算屯流噪声的部分。对于同相运放电路,电流噪声是通过流经R1和Rf并联后的等效电阻来体现的。这个关系可以通过运放的直流电流分析方法来推导得到。电流噪声乘以等效电阻Req,从而转换为输入相关电压噪声。我们来看看这个小例的具体参数值。 Example Current Noise Calculation PARAMCT ER OPA6273M, DP, SM UNITS MIN TYP MAX NoisE Der sit f=!0Hz 820压 f=10H E V/ H f: 10Hz 456 lo ltagc noisc, bw=0, 1 Hz to 1CHz 061564p Inout bias current noise oist Densit/, f=100Hz LA/Ha 30 16AH2」 Translating Current to Voltage Spectral Density 8)()=(164N12(09k=Dz Convert Spectral Density to rms: E1=√BW2=(001628:=0nVms Note: En: =0. 8nV is negligible compared to Env= 2497nV 电 TEXAS INSTRUMENTS e Here are the numbers. For this example the noise current density is very small, at just 1.6 fA/rtHz. The equivalent input resistance is also small, at approximately Multiplying these together, we get an extremely small noise voltage density of 0.0016n V/rtHz. Converting to RMs using the noise bandwidth, we get 0.8 n Vrms. For all practical purposes we could neglect this numbcr since it is insignificant compared to the voltage noise of 2497nv, but we will include it for the sake of completeness. Later we will see an example where current noise dominates ●这里提供了我们需要的参数。在这个示例中,电流噪声谱密度只有1.6 fA/rtHz,非常小。而等效输入电阻也很小,大约为1Kohm。两者相乘, 我们得到一个非常小的电压噪声谱密度值0.0016 nv/rthz。将其根据噪声带宽转换为RMS(均方根值),为0.8 n Vrms。从实际应用来看,相比于2497 norms的电压噪声,我们可以完全忽略这个非常不起眼的小噪声。但是这里为了展示完整的计算过程,我们仍然将其包括在内。后面我们会介绍一个以电流噪声为主的示例 Example Resistor Noise calculation Thermal noise r=V4kTR△=√4(138102)298K709k9(248kH)=2010nms Where R=R=E21|R=(1k2)(100k0)=09k △f=BW=248kL T=273+25C=298K (4kTR△f R1 Gain Req=R1‖|Rf TEXAS INSTRUMENTS 8 o Let's now finish up with calculating the circuit's resistor thermal noise, also called Johnson noise. We use the equivalent resistance to do this, which is just under 1k in our example. After plugging our values into the equation from the previous video, we get a result of 2010n Vrms. This is a significant amount of noise ●接下来我们将计算电阻热噪声,也被称为 Johnson噪声。我们将用到等效电阻Req,这个示例中为kohm。将其带入之前计过的公式,我们得到电阻热噪声为2010nVms。在这个例子中,这样的一个噪声值是非常大的! Total noise calculation val tage Nolse From Op-Amp RTE Eny-/r V rms current DIse trom op-Amp trans Eted to vol tage RI: En i=0. 80rYrIs Enr 2010nv rIns otal Noise rila E=2497807:1(072=325i Total Noise rto: 中 TEXAS INSTRUMENTS o Now that we have the op amp voltage noise, the op amp current noise translated to voltage, and the op amp resistor noise, we can add them together using the root sum of squares. this gives us the total input noise voltage in RMs Notice that the current noise does not contribute significantly to the total noise The opA627 is a FET input op amp which typically have very low input current noise densities o In this example, the total input-referred noise calculates out to 3205nVrms Multiplying by the gain of 101, we get an output noise voltage of 324uVrms Frequently engineers want to know the peak-to-peak noise. How do we compute this ●现在我们已经计算完毕电压噪声,转换为电压后的电流噪声,以及电阻噪声我们可以用平方和开根弓的方式来得到总的输入RMS噪声值。我们注意到, 在这个示例中电流噪声的贡献相较于总的噪声来说非常小。因为OPA627是个JET输入结构的运放,这种类型的运放一般具有非常低的电流噪声密度 ●在这个示例中,计算得到总的输入噪声为3205 n rms,乘以增益101VV, 我们可以得到总的输出懍声为324 aRms。通常工程师会想知道峰峰值噪声, 那么我们应该怎么计算呢?

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