Whether the spectrum that produces all frequency at the same time?

 

OK of course, white noise generator can produce all frequency with same range at the same time, simpler faster!

 

The noise in circuit is harmful normally, any good circuit should be outputted as far as possible low noise. Nevertheless, below certain circumstance, a character is clear and the output that the noise source that does not have other signal needs namely.

 

Circuit character is measured is this kind of circumstance. The output character of a lot of circuit can pass scanning inside certain frequency limits input signal and the response that observation designs will measure. Input scanning can input frequency or composition of sweep sine wave by disperse. Wave of clean sine of extremely low frequency (under 10 Hz) arise hard. Processor, DAC and filter wave can produce a few complex nicety relatively clean sine wave, but jump to every frequency rank, the system must be stabilized come down, make the ordinal complete scanning that includes a lot of frequency very slow. The disperse frequency with less test may be faster, but the risk that can increase the crucial frequency that jumps over place of tall Q phenomenon.
 

White noise generator is simpler than sweep sine wave, faster, because it produces all frequency with same range can efficiently at the same time. In the parts of an apparatus that be measured (the input end of DUT) brings to bear on the frequency that white noise can produce whole frequency limits to go up quickly answers general picture. Below this kind of circumstance, do not need generator of costly or complex sweep sine wave. Need to output receives spectrum analyzer repeatedly and observe DUT only can. Use more all be worth operation and longer collection time, the output on the target frequency limits of generation is answered more accurate.

 

The anticipation of DUT dialogue noise answers the noise that is frequency plastics. Use white noise to be able to expose an unexpected action quickly with this kind of means, for example barpque frequency stray, strange harmonic and the frequency that do not hope to appear answer bogus resembling.

 

In addition, attentive engineer can use white noise generator to check instrument. Flat noise curve should arise when the lab equipment that measures frequency to answer is measuring the white noise generator of foregone evenness.

 

Using a field actually, white noise generator is used easily; Volume is minor, enough realizes compact lab setting; Facilitate carry, suit the spot to measure; And the price is low. The high quality signal generator that has a large number of settings is very agile, very absorbing. But, versatility can hamper fast frequency is answered measure. Design good white noise generator not to need any control, can generate the output that can forecast completely however.

 

 

Resistor thermal noise, call noise of abdicate agreement writing or Nai Kui sometimes this special noise, it is by resistor interior charge is carried child hot faze movables is unripe. This noise is white noise roughly, be close to gauss to distributing. In electricity respect, noise voltage density gives out by next type:

 

VNOISE = √(4kBTR)

Among them:

KB is graceful constant of wave Er at present,

T is temperature (unit K) ,

R is resistor.

 

Noise voltage is cause by the random shift of the charge that has shed basic resistor (it is R roughly×INOISE) . Express the 1 a few example when showing 20°C.

 

Express 1. The noise voltage density of all sorts of resistor

 

 

Resistor of a 10 MΩ represents noise of voltage of broadband of a 402 NV/√Hz source and nominal resistor series connection. The change of R and T affects noise with square root form only, the resistor after magnifying so derives noise source quite stable, can check noise source as the lab. For example, from 20°C change is 6°C, resistor turns into from 293 KΩ 299 KΩ . The square root of noise density and temperature becomes direct ratio, the noise density change that because of the temperature of this 6°C change causes is relatively minor, it is about 1% . Same, to resistor, the resistor change of 2% causes the noise density change of 1% .

 

The consideration pursues 1: R1 of resistor of a 10 MΩ is in of operation amplifier carrying noise of generation white gauss. Resistor R2 and R3 magnify this noise voltage sends to output end. Capacitance C1 filter divides burr of charge of behead wave amplifier. Output is signal of white noise of a 10 μV/√Hz.

 

The gain in this exemple (1 + R2/R3) is taller, for 21 V/V.

 

Although R2 is very tall (1 MΩ) , coming from the R1 noise photograph after the noise of R2 and enlarge to compare also not matter.

 

Graph 1. The whole principle of white noise generator pursues. The Johnson of R1 of enlarge of LTC2063 of low drift small power comsumption noise.
 

The amplifier of circuit must be had enough low amount to carries voltage noise to the input, so that let R1,regard main noise as the source. The reason is resistor noise should the integral precision of dominant circuit, is not amplifier. Stem from same reason, the amplifier of circuit must be had enough low amount to carries voltaic noise to the input, in order to avoid (IN×R2) is adjacent (R1 noise×Gain) .

 

 

Watch 2 showed the noise that increases independent signal source to cause increases. Calculate by logarithm to the change of 502 NV/√Hz from 402 NV/√Hz have 1.9 DB only, or 0.96 power DB. 50% what operation amplifier noise is resistor noise about, the 5% uncertainty of operation amplifier VNOISE let output noise density to change only 1% .

 

 

 

White noise generator can use the operation amplifier of a resistor that can not produce noise only. The input end of amplifier of this kind of operation must have flat noise curve. But, noise voltage often cannot be defined accurately, and be mixed as production, voltage of temperature differ and have very big difference.

 

Circuit of other white noise may be based on job of neat accept diode, but its can forecast a gender to be not constant error. Nevertheless, to μA electric current, it is very difficult to search diode of optimal Qi Na to stabilize noise in order to obtain, be in especially low voltage (below <5V) circumstance.

 

White noise generator of a few high end is based on alignment of long pseudo-random binary system (PRBS) and special filter. Use small-sized controller and DAC the likelihood is enough; But, want to ensure DAC does not arise to build burr, harmonic or make tone product, the likelihood has experienced engineer talent to be competent only. Additional, choose the most appropriate PRBS alignment to also can increase complexity and uncertainty.

 

 

The white noise generator that ● uses easily must be portable, use batteries power supply namely, this means its must be equipment of electron of small power comsumption.

● generator must offer even noise output, even if frequency reachs above under 0.1 Hz.

 

Considering treat of of afore-mentioned condemn of a confusion of voices these keys limit a condition, amplifier of 0 drift operation accords with LTC2063 low power comsumption this one requirement.

 

Graph 2. Pocket model white noise generator is archetypal
 

10The noise voltage of MΩ resistor is 402 NV/√Hz, the noise voltage of LTC2063 is its half about. The noise electric current of 10 MΩ resistor is 40 FA/√Hz, the noise electric current of LTC2063 is less than its half. The typical source current of LTC2063 is 1.4μA, and voltage of total power supply can fall to 1.7 V (rated voltage is 1.8 V) , because this LTC2063 is right,batteries application is very ideal. According to the definition, low frequency measures the set-up time with very long need, accordingly this generator must by batteries long power supply.

 

LTC2063 inputs the noise density of end to be 200 NV/√Hz about, noise can be forecasted inside whole frequency limits and maintain evenness (±0.5 DB less than) . 50% what assume the noise of LTC2063 is thermal noise, and noise of operation amplifier voltage is changed 5% , output noise density to be changed only 1% .

 

The design makes sure amplifier of 0 drift operation does not have 1/f noise. Some parts of an apparatus are compared other better, and commonner is, broadband norms mistake or the value that 1/f noise outclass gives out in data manual, especially to voltaic noise. The curve of data manual noise of amplifier of operation of a few 0 drift won’t drop MHz frequency extent, the likelihood is to mask 1/f noise. Behead wave stabilizes operation amplifier may be to settle way, it can let noise maintain evenness when ultralow frequency is led. Additional, high frequency noise is raised must not damage property with switch noise. The data that shows here supports use LTC2063 to answer these challenges.

 

 

Filmy R1 (Vishay/Beyschlag MMA0204 10 MΩ) produces major noise. MMA0204 is a few a few hold concurrently high quality one of 10 MΩ choices with low cost. In principle, r1 can be any 10 MΩ resistor, because signal electric current is very small, so but oversight 1/f noise. To the main element of this generator, had better avoid to use the chip of low cost thick film with precision or doubtful stability.

 

To gain optimal precision and long-term stability, r2, R3 or RS can be 0.1% filmy resistor, for example TE CPF0603. C2/C3 can be one of most dielectric capacitance; C0G is usable will assure small leakage current.

 

Graph 3. Unit position
 

 

R1/C1/R3 of annulus road area should be decreased to the smallest, in order to ensure EMI controls function optimal. In addition, r1/C1 should try very good screen, in case electric field influence, this will think to discuss further partly in EMI. Although not be very crucial, but R1 should avoid bigger temperature change. Had good EMI screen, hot screen often is enough.

 

Should avoid the LTC2063 course inside VCM limits to input voltage transition area to course, because hand in,arise more possibly taller and the noise with poorer stability. To achieve optimal result, v+ should use 1.1 V at least, input in all modular voltage is 0.

 

Ask an attention, the RS of 10 KΩ appears very tall, but LTC2063 of small power comsumption has higher output impedance, although 10 KΩ also won’t output LTC2063 the laden capacitance of end with its,solve Ou completely. To circuit of this white noise generator, bringing about the electric capacity of a few output that the peak changes can be design character, is not dangerous.

 

Outputting what end sees is 10 KΩRS and a 50 NF receive ground capacitance CX. This capacitance CX will with LTC2063 circuit interaction, bring about frequency to answer occurrence peak to change. This peak changes the even bandwidth that can use patulous generator, like enlarging the lower end with respect to the eyelet in resembling loudspeaker. Use tall impedance load suppose (> 100 KΩ) , because laden meeting is showing low impedance to reduce output n, and affect a peak possibly still change.

 

 

Be in high frequency when be restricted to be worth, have parameter of a few IC (for example ROUT and GBW) meeting influence evenness is spent. If do not use signal analyzer, the commendation of CX is worth for 47 NF, this can produce 200 Hz normally the bandwidth to 300 Hz (-1 DB) .

 

Nevertheless, CX can be spent in the light of evenness or bandwidth undertakes optimizing, typical cost comes for CX = 30 NF 50 NF. Want to obtain wider bandwidth and higher peak value, use lesser CX please. Should make answer attenuation faster, use bigger CX please.

 

Crucial IC parameter and operation amplifier source current are concerned, the parts of an apparatus of small source current may need largish CX, and the electric capacity that the parts of an apparatus of tall source current needs probably to be less than 30 NF, realize wider even bandwidth at the same time.

 

The curve here is outstanding showed how CX value affects closed circuit frequency to answer.

 

 

Output noise density and CX (RS = 10 KΩ , ±2.5 V power source) the relation is shown 4 times like the graph. Output RC filter can eliminate clock noise effectively. This graph showed the concern of the output when CX = 0 and CX = 2.2 NF/10 NF/47 NF/68 NF and frequency.

 

Graph 4. The graph shows the output noise density of the design 1 times
 

Slight peak is shown to change when CX = 2.2 NF, and Shi Feng of CX = 10 NF is changed the strongest, increase to drop gradually as CX next. The trace of CX = 68 NF shows change without the peak, but even bandwidth is apparently inferior. Optimal result is CX when be 47 NF about; Clock noise is lower than signal n 3 amounts class. Because perpendicular resolution is finite, cannot judge output extent evenness accurately to spend the relation with frequency. This graph uses generation of power source of ±2.5 V batteries, but the design allows to use two buttons cell (make an appointment with ±1.5 V) .

 

Graph the evenness after the Y axis of 5 expresses enlarge is spent. To a lot of application, the evenness of 1 DB less than is spent use quite namely, <0.5 DB is more typical. Here, CX = 50 NF is optimal (RS = 10 KΩ , VSUPPLY±1.5 V) ; CX = 45 NF, nevertheless 55 NF also can be accepted.

 

Graph 5. The graph shows the enlarge view of the output noise density of the design 1 times
 

High resolution evenness is spent measure need time; To this curve (10 Hz arrives 1 KHz, average 1000) , every trace costs 20 minutes about. Standard solution uses CX = 50 NF. Shows 43nF, 47nF and 56nF trace (all CS<0.1% tolerance) spend with optimal evenness the photograph is very smaller than having but apparent deviation. The orange curve that adds CX = 0 raised even bandwidth with showing the peak is changed (to Δ= 0.5 DB, raise 380 Hz from 230 Hz) .

 

To capacitance of apropos 50 NF, establish ties 2×0.1μF C0G may be the simplest solution. 0.1μF C0G 5% 1206 is bought very easily from Murata, TDK and Kemet. Another kind of choice is 47 NF C0G (1206 or 0805) ; This parts of an apparatus is smaller, but the likelihood is so not common. The place before be like is narrated, optimal CX follows actual IC parameter and change.

 

We still checked evenness to spend the relation with power source voltage, refer to a graph 6. Standard circuit is ±1.5 V. When power source voltage the change is ±1.0 V or ±2.5 V, the peak is changed have minor change, evenness is spent also have minor change (let power supply because of VN and change, thermal noise is dominant) . Inside limits of voltage of whole power source, the change that the peak is changed and evenness spends all is make an appointment with 0.2 DB. This curve makes clear, when circuit by two when small cell power supply, extent stability and evenness are spent good.

 

Graph 6. All sorts of power source voltage output noise density correspondingly
 

Archetypal to this, when power source voltage is ±1.5 V, evenness is spent in 0.5 DB less than, frequency is highest it is 380 Hz about. Below ±1.0 V power source, evenness is spent and the peak is changed increase somewhat. Come to ±1.5 V voltage of ±2.5 V power source, output n did not change apparently. Total Vp-p (or V Rms) output n depends on fixed 10μV/√Hz density and bandwidth. This archetypal output signal is 1.5 MV P-p about. In certain low-down frequency (MHz limits) , noise density may exceed formulary 10μV/√Hz. Archetypal to this, had confirmed when 0.1 Hz, noise density still maintains in 10μV/√Hz.

 

With respect to stability and temperature character, thermal noise takes dominant place, accordingly to T = 22 (±6)°C, extent change is ±1% , this one change is almost sightless on the graph.

 

 

This prototype use belt gets together acyl inferior the small Copper Foil of amine insulation layer regards screen as the layer. This foil piece or ala piece twine inputting component (all round 10 M + 22 PF) , solder to be carried to the ground connection of PCB the reverse side. Change ala piece the position is mixed to EMI sensitivity low frequency (LF) stray risk has distinct effect. The experiment makes clear, now and then occurrence low frequency stray is caused by EMI, this stray can prevent through first-rate screen. Use ala piece, in do not have any adding to guide the circumstance of magnetism alloy screen falls high, the prototype response in the lab is very clean. Did not appear on spectrum analyzer advocate power source noise or other stray. If much noise has appeared on signal, need additional EMI screen possibly.

 

When using cell of and rather than of exterior power source, in all modular electric current is added very easily to signal. Suggest the instrument ground connection and sincere lead join, use CM choke in the power supply line of generator.

 

 

Always a few application need more bandwidth, for example complete frequency limits or ultrasonic limits. Below the source current of a few μA, taller bandwidth is not actual. By right of about 300 Hz comes the even bandwidth of 400 Hz, the 50 Hz/60 Hz that is based on the circuit of LTC2063 resistor noise to be able to be used at checking certain instrument advocate power source frequency, for example seismic radiodetector application. This limits suits to check all sorts of VLF application (for example sensor system) , because frequency limits is low,come 0.1 Hz is the following.

 

Output signal n is inferior (<2 MV P-p) . Follow-up LTC2063 configuration is the inphase amplifier that has 5 times gain, add on another RC to output filter, can offer output of likewise controlled noise of 300Hz even broadband, and range is bigger. In cannot make range of closed circuit frequency the biggest below the case that turn, the capacitance of two end can reduce feedback resistance integral bandwidth. Below this kind of circumstance, the brim that the influence of RS and CX answers in closed circuit is lesser, negligible even.

 

 

The white noise generator that article place narrates is a kind small-sized but main tool. As the extension that measures time, the standard instrument —— of low frequency application a kind of simple, reliable, portable equipment, almost OK character of the instantaneous circuit that finish measures —— to make the welcome compensatory tool in engineer kit. Differ with the complex instrument that has numerous setting, this generator does not need user manual. The source current of this kind of special design is very small, this to long VLF application measures medium batteries power supply the operation is crucial. When source current is very small, do not need switch. The generator that uses batteries job still can prevent in all modular electric current.

 

The LTC2063 low power comsumption that uses in this design the key that amplifier of 0 drift operation is requirement of contented project limitation. Its support uses the noise that magnifies by circuit of amplifier of simple and inphase operation to produce resistor.