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vca824 VGA

Lisong Xu1
Prodigy 160 points
Other Parts Discussed in Thread: VCA824, VCA822

I want use VCA824 to design a VGA cuicuit, which is liner in V/V,

transfor function is as follow:

Vo=AVg*Vi

Vi from 0V to 5V,

Vo from 0V to 5V,

AVg chandges from 0V to 5V,

Can VCA824 do the work?

Can the curcuit of Figure76 in datasheet do the work?

  • 0
    TI__Genius 13935 points

    Hello Lisong,

    You circuit cannot be implemented on +-5V supplies.  The input range (-2.1V to +1.6V) is too small and the output range also won't make it to 5V on a +-5V supply (+-3.6V guaranteed at room temp).

    Also, the gain voltage only ranges from -1.2V to +1.2V (Figure 4). 

     

    If you want to support input and output voltages of 0V to 5V you will need a power supply of 10V centered on 2.5V, so a negative supply of -2.5V and +7.5 V.  There is some flexibility in these voltages, but they need to be close.

     

    If you set up on a +7.5V -2.5V supply the gain control voltage will range from  1.3V to 3.7V. 

     

    If it is possible for you to AC couple your signal you can use the circuit in Figure 75 but you will still need to respect the gain control voltage of -1.2V to +1.2V.

     

    Regards,

    Loren

  • 0 in reply to Loren Siebert 1
    Prodigy 160 points
    In the datasheet，it says that VCA824 and VCA822 can use +—5V voltage supply.
    In the datasheet, is also says VCA824 can be used as four-quadrant multiplier. There is a cuicut in Figure 76.
    Now the question is if I use it as Figure 76.
    the input voltage range?
    the output voltage range?
    the control voltage range?
  • 0 in reply to Lisong Xu1
    TI__Genius 13935 points

    Hello Lisong,

    The values you requested are in the datasheet and in my previous post.  The circuit of Figure 76 does not change the input/output voltages of the amplifier. 

    Regards,

    Loren