How do tall gain and tall bandwidth hold concurrently?
[introduction] because we must use many power level, realize tall gain at the same time consequently (1000 – V/V and even taller) with tall bandwidth (tens of MHz) the likelihood is a kind of challenge. Besides the circuit requirement of respect of tall gain, tall bandwidth, still need to pay close attention to noise and stability problem mainly.
Examine next figures, understand the overall framework of 3 class amplifier.
The noise that every successive amplifier produces and the noise that before one class produces are added always mix for RMS, the gain that uses latter power level next undertakes increasing advantageous position. To framework of a 3 class, its noise can express to be:
And the product that gain is various gain, following place show:
So far, we had circuit framework and two equation, but not detailed still introduction uses program actually. According to noise equation, the first class will become restricted factor.
The blame that to the graph a shown tall gain configures inputs class noise instead, usable computation leaving type:
Graph 1: Simplify noise model
With respect to present circumstance character, we need to choose a kind of amplifier that has lowermost voltage noise. Because we want to still hope to maintain good bandwidth while the first class realizes highest gain, so we will deliver the view to have highest gain bandwidth to accumulate (the amplifier of lowermost voltage noise of GBWP) . Undertake parameter is searched simply, achieve following result.
Because we hope to develop + 5-V system, consequently we can choose LMH6629 for the first class. Below the case that wins 50-V/V gain, still have 78MHz bandwidth.
Of course, we also can choose identical LMH6629 for any other class, but need not resemble the first stage as a result of the norms of input voltage noise of other form strict in that way, consequently we can enlarge search limits further, use any parts of an apparatus that can realize tall bandwidth and tall gain. Voltaic feedback amplifier and maintaining bandwidth to be here basically at gain independently is optimal choice undoubtedly. Refer to detailed issueing a list to list detailed list please.
Highest bandwidth solution
Here, we can need bandwidth to consider according to amplifier and place is to choose to turn over photograph or blame to turn over photograph gain circuit. OPA695 can realize lower noise in be configured instead, and OPA683 and OPA684 can be in be not the implementation in be being configured instead lower noise.
Because we plan to realize tall gain on only course (100-V/V) , consequently gain resistor but low to 10W. In turn over photograph develop to attack in the structure, this may be caused to drive class restrict additionally. Gain resistor should be maintained between 10W and 50W, and feedback resistor should not exceed 1.5KW. Be sure to keep in mind, resistor of feedback of frequency noisy merit (RF) limitation, and feedback capacitance (because of,CF) the utmost is met position of package, board side create parasitism feedback electric capacity.
It is each bits of afore-mentioned application in circuit, replace a plan 1 medium ideal amplifier, get the picture below 2.
Graph 2: 100 of executive 10MHz bandwidth, 000-V/V multistage amplifier.
Can be in various between insert RC filter, reduce the noise of a generation with utmost ground. We can answer overall frequency and – 3dB bandwidth plans to synthesize 6 rank the utmost [1] .