استخدام الترانزستور (fet) تأثير المجال في مكبرات rf .. كتاب التلفزيون الملون والعادي

5-5 Using the Field Effect Transistor (FET) in RF Amplifiers:

It is used in modern circuits, especially in RF amplifiers - and this transistor has two types, JFET, i.e. with a link.

​​​​​ IGFET, i.e., with an isolated gate, and is called MOSFET, Figure (5-15). The JFET transistor has two types, according to the semiconductor materials used in the connection between the elements. They are the positive or negative channel N-Channel.P-Channel and the use of the FET transistor which is a unipolar element and not bipolar Bipolar as is the normal transistor, because the passage of current through it is through the flow of electrons or gaps. As for the FET or Mosfet transistor, it is done by one method, and this reduces noise and distortion when used as an amplifier at high frequencies, and the input impedance is very large, so it is similar to the valve, and thus the input signal current (gate) is very small. It also has another advantage as the current passing through it is directly proportional to the square of the gate voltage - this is what makes the output of the amplifier rich in second harmonics, while the normal transistor or valve is rich in third and higher harmonics in addition to the second harmonic. Because its linear magnification is most likely. This is what weakens the output signal, especially when modulating, and therefore it is preferred in the mood circuit.

5-6 Using the Mosfet to amplify the VHF field:

The diagram shows Figure (5) - (17) the simplified circuit for using a dual-gate Mosfet with two gates in the VHF amplification circuit, the very high frequencies of the voter, in which the AGC voltage is obtained through the voltage divider R2, R1 and R2, and the capacitors filter the AGC voltage to make the direct current DC Most of it applies to the second gate of the transistor (G2). As for the RF signal, it is applied through the capacitor and C and elicited via R3 - and the signal voltage appears on the first gate (G). Thus, the current of the Fet transistor is set by two voltages, namely the AGC voltage and the signal voltage - as for the upstream bias, it is secured by means of R, and C is used to prevent feedback - and is taken The output signal from the secondary of the transformer T in the bank circuit.

MOSFET use in UHF field amplification:

The diagram shows Figure (4) - (34) the simplified circuit for using a dual-gate MOSFET transistor to amplify the UHF field - AGC voltage is applied to the second gate G2, after winding the coil L24 and the capacitive binary (fractor) CR13. The UHF signal coming from the antenna is applied to the first gate G1 through the capacitor C43, and the antenna input coil L23 is inductively connected with the L24 coil, as well as the L29,127 coils, which form a link stage between the RF amplifier and the mixer, as they are connected in an inductive and capacitive manner, and these coils are tuned by the capacitive diode CR14 and CR15 in sequence - as for files 24 - 27 - 29 - they are placed on a printed copper circuit - and as for tuning, it is controlled by moving a piece that carries capacitors C96- C68- C67 that are proportional to the induction files.