Improved differential amplifier circuit The constant current source circuit not only sets a suitable quiescent operating current for the differential amplifier circuit at a low power supply voltage, but also greatly enhances the common mode negative feedback effect, so that the circuit has a stronger ability to suppress common mode signals. As shown in the upper right figure, the constant current source circuit can be replaced with a constant current source. In the actual circuit, a potentiometer with a very small resistance is usually added between the emitters of the two tubes, see Rw in the figure below. Zero-adjusting potentiometer Rw: adjust the sliding end position of the potentiometer to make the circuit when uI1 = uI2 = 0, uO = 0, Rw is called zero-adjusting potentiometer.
Slide Switches
The Slide Switches is used to switch the circuit by turning the switch handle to turn the circuit on or off. It is different from our other serious switches, for example, Metal Switches, Automotive Switches, LED light Switches, Push button Switches, Micro Switches, The commonly used varieties of Miniature Slide Switches are single pole double position, single pole three position, double pole double position and bipolar three position. It is generally used for low voltage circuits, featuring flexible slider action, stable and reliable performance. Mainly used in a wide range of instruments, fax machines, audio equipment, medical equipment, beauty equipment, and other electronic products.
The Mini Slide Switches are divided into: low-current slide switches (right), and high-current slide switches (left). Small current slide switches are commonly used in electronic toys, digital communications. High current is generally used in electrical appliances, machinery, etc.
It can divided into 4 types modals, respectively are:
1. High-current sealed switch
Its rated current is as high as 5A, and it is sealed with epoxy resin. It is a large current sealed switch. It has a variety of terminal forms, contact materials are silver, gold, switching functions. Therefore, there are many types of subdivisions. Widely used in electrical appliances and machinery
2. Single sided snap-on surface mount type slide switch
The actuator is operated on the side and the pins are patch-type, so it is a unilateral spring-back surface mount type slide switch. Widely used in communications, digital audio and video
3.4P3T in-line slide switch
The contact form is 4P3T and the pin is in-line. It is 4P3T in-line slide switch. 4P3T determines that it has 8 pairs of pins. At the same time, there are two pairs of brackets that support, fix, and ground. Widely used in building automation, electronic products
4.Long actuator jacking type slide switch
Actuator 12mm, and located at the top of the switch, it is a long actuator jacking type slide switch. Widely used in digital audio and video, various instruments / instrumentation equipment
Slide Switches,Micro Slide Switch,2 Position Slide Switch,Momentary Slide Switch YESWITCH ELECTRONICS CO., LTD. , https://www.yeswitches.com
In the differential amplifier circuit, increasing the resistance of the emitter resistance Re can improve the common mode rejection ratio. However, it is not easy to make large-resistance resistors in integrated circuits; the use of high-resistance Re requires a high-regulated power supply, which is not suitable. If the quiescent current of the emitter of the transistor is 0.5mA, the current in Re is 1mA. When Re is 10kΩ, the value of the power supply VEE is 10.7V. Under the same quiescent operating current, if Re = 100kΩ, the value of VEE is about 100V. 
In order to use both a lower power supply voltage and a large equivalent resistance Re, a constant current source circuit can be used instead of Re. When the transistor works in the amplifying area, its collector current is almost determined by the base current and has nothing to do with the tube voltage drop. When the base current is a constant DC current, the collector current is a constant current. Therefore, to replace Re with an operating point stabilization circuit, the circuit shown in the upper right diagram must be used. 
In order to obtain a differential amplifier circuit with high input resistance, the transistor can be replaced with a field effect transistor, as shown in the upper right figure. This type of circuit is particularly suitable as an input stage for directly coupled multi-stage amplifier circuits. Generally, the input resistance can be regarded as infinite. Its application is the same as the transistor differential amplifier circuit.
