Data is collected, the other application with sensor signal recuperation and input signal bigger span, can ask to use gain optional amplifier. Optional amplifier is in traditional gain in feedback annulus road, it is to use switch to reach resistor join to be inputted instead, nevertheless switch resistor can reduce the noise performance of amplifier, increased to input the capacitance that go up instead, and rose nonlinear gain error. When using low noise amplifier, the addition of noise and capacitance, nonlinear gain error, all accuracy that these metropolises affect nicety application.

 

 

Graph 1. Use ADA4896-2 and ADG633 compose to build low noise gain optional amplifier comes drive low block is laden
 

The graph shows gain 1 times the switch technology that optional amplifier used a kind of innovation, can hold the property of 1 NV/√Hz noise of ADA4896-2, reduce at the same time nonlinear gain error. Use this kind of technology, the user can choose the switch with the smallest electric capacity to make the bandwidth of circuit the biggest change.

 

The switch that through ADG633 switch of 3 SPDT CMOS realizes uses the following configuration: S1A and S2A at the same time open, or, s1B and S2B at the same time open. Switch S1 joins the output to feedback resistor is carried, switch S2 is in V1 or V2 undertakes sampling, in this part dot switch resistor does not affect gain. Can reduce gain error so, make sure noise function is changeless at the same time. Below place indication, gain of amplifier of the first class is 4V/V (“A” switch open) or 2 V/V (“B” switch open) . The amount of switch gain can try to expand through increasing switch, also can pass multichannel answer to use implement (like 4:1ADG659 or 8:1ADG658) undertake expanding.

 

Ask an attention, those who output bumper to had shed S2 sampling switch is nonlinear guide the input of electrify block slants buy electric current will arise maladjusted. To compensate this maladjusted, beard general untapped switch (in the feedback method of bumper of S3B) park output.

 

Additional, input amplifier slant what buy electric current can cause because of gain surprise is maladjusted. Because input amplifier and output bumper to use same chip, because this can use its,slant of buy electric current match a gender to eliminate afore-mentioned maladjusted change relatively. The resistor of the poor value that is equal to a size RF2 and RF1 and switch S2A establish ties, can decrease maladjusted – voltage is poor. The derivation formula below explains, in V1 sampling can produce wants signal gain, and without gain error. RS expresses switch resistance. V2 can use same method to derive.
 

 

equation 1 generation enters equation 2 can get,

 

 

Attention, if VO1 produces wants signal gain and without gain error, criterion amortize output VO2 also does not have gain error. The graph shows the normalization frequency that is in in VO2 for circuit 2 times to answer.

 

Graph 2. The frequency of VO2/VIN is answered