1. Technical Field
The present disclosure relates to amplifier circuits.
2. Description of Related Art
Amplifier circuits are a necessary part of audio equipment, such as, a tape recorder, a radio, or a media player. Usually, the amplifier circuit includes a special amplifier chip and corresponding peripheral circuits. As shown in
Therefore, it is easy to know the amplification factor of the amplifier circuit 1 is equal to R1/R3=R2/R4=15. However, in general, the resistors R1 and R2 of the amplifier circuit 1 are Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) mode resistors, such as resistors between source and drain of the MOSFET, when the conduction degree of the MOSFET resistor is different, the resistance value of the MOSFET resistor is different. Therefore, the resistance values of the resistors R1 and R2 are difficult to control to a certain value. Usually, the actual resistance value of the resistors R1 and R2 have 20% bias compare to ideal resistance values of the resistors R1 and R2, and the resistors R3 and R4 are normal resistors, such as metal resistors and the resistance value of the R3 and R4 can maintain a certain value and equal to their ideal resistance values. Therefore, the actual amplification factor of the amplifier circuit 1 would be in the range from 300*(1−20%)/20=12 times to 300*(1+20%)/20=18.
However, if the amplification factor is not great, such as 12, the gain of audio signals output by the audio source is insufficient, if the amplification factor is too large, such as 18, the speaker has the risk of damage.
Therefore, it is desirable to provide an amplifier circuit to overcome the above-mentioned limitations.
Many aspects of the present disclosure should be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
Embodiments of the present disclosure will now be described in detail below, with reference to the accompanying drawings.
Referring to
In the embodiment, the resistors R5 and R6 are MOSFET mode resistors, the resistors R7 and R8 are normal resistors. The sum of the ideal resistance values of the resistors R5 and R7 is equal to the resistance value of the resistor R3 of
The amplification factor of the amplifier circuit 1′ is R1/(R5+R7)=R2/(R6+R8), if the resistance values of the resistors R1, R2, R5, R6 have no bias, namely equal to the ideal resistance value, the actual resistance values of the resistors R1, R2, R5, R6 are equal to the ideal resistance values of the resistors R1, R2, R5, R6, then the amplification factor of the amplifier circuit 1′ is 300/(10+10)=15. As described in background, the resistance values of the resistors R1, R2 have bias less than 20%, namely the actual resistance values of the resistors R1, R2 are located in the range from 300*(1−20%) to 300*(1+20%). Because the resistance values of the resistors R5, R6 have the same bias as the resistor R1, R2, then the actual resistance values of the resistors R5, R6 are located in the range from 10*(1−20%) to 10*(1+20%). Therefore, the actual amplification factor of the amplifier circuit 1′ is located in the range from 300*0.8/(10*0.8+10)=13.3 to 300*1.2/(10*1.2+10)=16.36. Compare to the range of the actual amplification factor of the amplifier circuit 1 of
It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being exemplary embodiments of the present disclosure.
Number | Date | Country | Kind |
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201010619563.0 | Dec 2010 | CN | national |