* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Differential Amplifier
Survey
Document related concepts
Control theory wikipedia , lookup
Power inverter wikipedia , lookup
Current source wikipedia , lookup
Audio power wikipedia , lookup
Flip-flop (electronics) wikipedia , lookup
Public address system wikipedia , lookup
Scattering parameters wikipedia , lookup
Integrating ADC wikipedia , lookup
Buck converter wikipedia , lookup
Signal-flow graph wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Control system wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Regenerative circuit wikipedia , lookup
Schmitt trigger wikipedia , lookup
Two-port network wikipedia , lookup
Wien bridge oscillator wikipedia , lookup
Current mirror wikipedia , lookup
Transcript
Technical Info Differential Amplifier A differential amplifier amplifies the voltage difference applied to two inputs. An example of a configuration of the amplifier is a connecting the emitters of two transistors with equal characteristics as in Fig. 1. The voltage difference applied to the base of these transistors is amplified. Fig. 2 shows the waveform of each node in Fig. 1. The output of differential amplifier circuitry shown in Fig. 1 is further amplified and applied utilizing negative feedback. High performance and inexpensive differential amplifiers, so-called operational amplifiers (Integrated circuit), are available in the market. +V R1 ein1 R2 eout1 eout1 ein2 eout2 eout2 Input ein2 ein1 Output eout1 - eout2 Differential Output Figure 2. Waveforms -V Figure 1. A differential amplifier circuitry If two input signals of the differential amplifier are the same, the (differential) output will be nearly zero. That is, common-mode noise of the input is greatly attenuated, and only the signal is amplified. A function of the amplifier to reduce the common-mode noise is CMRR (common-mode rejection ratio) / Technical Info Differential Amplifier The gain when negative feedback is delivered to the differential amplifier (op-amp) is the following equation. ei In Fig. 3 e = ei - β・eo e・Ao = eo From both equations, the output voltage eo is Ao eo = × ei 1 + A・β o + e - Ao eo R1 if Ao · β is much larger than 1, e o = ei ÷ β The gain A when negative feedback is applied is 1 R +R e A= o = = 1 2 ei β R2 The gain is determined by the value of β. R2 β circuit Figure 3. Differential Amplifier configuration using a negative feedback circuit The matching of two transistors is essential to achieve optimum differential characteristics in the circuit, Fig 1. Therefore, we would integrate them into one chip, utilize dual transistor, or sort individual parts strictly. NF could even balance unequal characteristics transistors with our negative feedback technology to achieve optimum differential characteristics (Fig 4). Our amplifiers, SA-420F5, SA-421F5, and SA-430F5 meet the world's highest standards of low-noise characteristics using our technologies above. VCC Output 1 + - Output 2 8 FETs mounted on both sides of a substrate Input 1 + Input 2 Vref Vee Figure 4. A differential amplifier circuitry which performs optimum differential characteristics even with discrete parts Figure 5. “SA-421F5” Differential FET Amplifier achieves 0.5 nV/√Hz equivalent input noise density