Tall gain, big bandwidth, why can circuit still produce vibration?
[introduction] be in before “ tall gain, tall bandwidth, how both hold concurrently? In one article of ” , while if why realizing tall gain and tall bandwidth,we were discussed, still can keep enough tall letter a confusion of voices is compared (SNR) . We discuss more detailed ground executive method and the issue that produce possibly in this article.
Because target gain is very tall, need to check dc above all (the circumstance that DC) works, whether output deflection voltage is in with examining set limits less than beforehand. The range that if exceed gain level and amplifier dc parameter, input to slant,buy electric current and input deflection voltage set beforehand, criterion circuit is put apparently possibly in oscillation. Systematic oscillation is reflected for a variety of forms, if noise increases, output deflection voltage and issueing static electric current to increase without laden circumstance etc, by no means an isolated case.
If produce oscillation, circuit to be coupling of tall gain dc and various job is regular, criterion coupling of each class hand in change electric current (voltage of deflection of output of AC) meeting general regards as potential problem is masked. The question that leaves exclusively now removes undesirable parasitism character namely.
In road of annulus of make a present of of existence positive and negative, or when the phasic abundant when the system spends inadequacy, can produce vibration. Because amplifier itself is in steady state and load is block sex, the reason of only possibility is road of annulus of make a present of of existence positive and negative.
The following circuit that the graph shows 1 times can lead the noise gain below to handle bigger DC deflection in low frequency through adjusting amplifier. From this, any dc heft are 1-V/V only in the gain that outputs end. In addition, graph 1 still indicating power supply is to pass connective of power source layer. The by-pass capacitor of this locality power source of every amplifier gave out in the graph, but to simplify for the purpose of omited by-pass capacitor of global power source.
Graph 1: Take the multistage amplifier principle of power source layer to pursue
Just think, not class is weighing load in drive, electric current will flow into load from power source. This electric current will be caused to power source course disturb. Because the power source course of multistage amplifier joins together, we will be aware of this kind to disturb with the 2nd class in the first class. Disturb the output that can appear in the first class, only the power source of the first class is restrained than (PSRR) is OK damply, magnify by the 2nd class and the signal gain of the 3rd class again next.
If disturb,the PSRR of frequency is mixed under the 2nd class the product of gain of the 3rd class, of so laden generation disturb to be able to be magnified. Change character, road of annulus of make a present of of positive and negative exists on power source course.
Settlement method is very simple, have the board side position of circuit board meticulously, let power source give first not class power supply, be in at the same time various between insert inductor of a series connection. In the 3 class amplifier that shows in place laying a plan, we added two inductor to every power source only. In the graph 2 in, we implement this kind of method on positive electricity source only. Attention, negaive electricity source also may need such processing.
Graph 2: Be in various a segregation of executive power source
The model that the graph shows 2 times used LMH6629 to serve as the first class, OPA684 is mixed as the 2nd class the 3rd class.
Use + the even frequency band that 5V power source can realize good 5MHz, – 3dB bandwidth is 10MHz. To 10uV signal, it is in magnifying power 100, below the circumstance of 000V/V, gotten SNR is about 12dB.
Graph 3: The frequency after every class is answered