subject: Precision low-noise amplifier and offset circuit technology - precision amplifier circuits - electronic [print this page] Precision low-noise amplifier and offset circuit technology - precision amplifier circuits - electronic
1 Status Operational Amplifier Op amp since its inception in 1963, come a very long development path, and linear systems for all parts of the de facto standard. Almost every major Semiconductor Manufacturer's product line are operational amplifiers this product. Depending on the application needs a universal key differentiation, low voltage / low power consumption, high speed type, high-precision op amp type four major categories of products. Current amplifier performance levels have reached the following targets, which in the 20th century, 60 years is unheard of: a bandwidth exceeding 1GHz; conversion rate of more than 5 000 V / s; operating current less than 10 A; working voltage as low as 0.9V; input offset voltage less than 20 V. 2 Precision Amplifier Precision amplifier generally refers to less than 1mV offset voltage op amp, the use of the process, he stressed the circuit is low noise and low offset performance. With the new Sensor Technology (such as missile gyroscope, MEMS MEMS Sensor Etc.) for promoting the use and improvement of performance of the whole, the type of precision operational amplifiers and bandwidth have a higher demand. To meet this demand, foreign IC Has launched a number of broadband products. 3 low-noise offset circuit technology New sensor precision op amp applications put forward higher requirements on the micro-sensor, because its output was primarily in the low frequency signal, and the signal amplitude is small, the imbalance caused by CMOS technology and low-frequency 1 / f noise increased, Micro Sensor Circuit presented a great challenge. CMOS process to achieve the next generation the same dynamic range, the circuit needs to maintain the greatest possible output swing, and the use of a variety of technology to reduce offset voltage and 1 / f noise. Present, the mainstream to achieve low offset, low noise circuit techniques are: self-stabilized AZ (autozero) technology, correlated double sampling CDS (CorrelatedDoubleSampling) technology and chopper-stabilized CHS (ChopperStabilization) technology. In this paper, AZ and CHS technology. 3.1 from zero technique (AZ) The basic principles of
3.1.1 AZ From zero technique (AZ) The basic idea is to first sample and save the noise and offset, then its input or output from the transient signal in addition. Of course, can also be added between the input and output ports to achieve an additional noise and offset of zero. If the noise signal is not changing with time signals (such as DC disorder), he will be eliminated; If it is a slowly varying low-frequency random noise (such as 1 / f noise), will be the high-pass filter. The principle shown in Figure 1, assuming that enter the reference offset voltage Vos, enter the reference noise VN. AZ process is divided into two stages: the first stage, the signal is isolated, AMP input is shorted, the role of the sampling pulse, the input offset Vos and sampled noise VN and saved, and to negative feedback in the form of introduction from the port N , the output is controlled in a very small margin; the second stage, signal access, if the assumption Vos and VN and sampling the same, then the noise and offset will be eliminated. 3.1.2 AZ on the impact of noise
(1) the impact of white noise Assumed operational amplifier equivalent input white noise is equivalent to-3dB bandwidth of fc in the low-pass characteristics (LF) noise, the sampling frequency fs, is usually fc>> fs, AZ's output of white noise can be approximated as:
