AN3680| Application Note
Maxim/Dallas > App Notes > AMPLIFIER AND COMPARATOR CIRCUITS Keywords: Direct Drive video amplifier, Reconstruction filter
VIDEO CIRCUITS
Nov 01, 2005
APPLICATION NOTE 3680
Implementation of a DirectDrive Video Filter Amplifier's Negative Charge Pump and Analog Switch in Audio/Video Applications
The MAX9503/MAX9505 DirectDriveTM video filter amplifiers integrate an analog switch (MAX9505 only) and a negative charge pump that can be used to improve performance for audio/video applications.
Description
The MAX9503/MAX9505 DirectDrive video filter amplifiers integrate an analog switch (MAX9505 only) and a negative charge pump. These devices operate from a single 2.7V to 3.6V power supply. They can be directly connected to the output of the video DAC and set the black level of video signal to ground at its output. They eliminate the extra negative voltage supply and large output DC-blocking capacitors, thus saving cost and board space. The negative charge pump and the analog switch can be used to improve performance in audio/video applications, as discussed in the following text.
Adjusting the Sync Tip Voltage by Using the Negative Charge Pump
The MAX9503/MAX9505 expect the input sync tip signal to be between 0 to 50mV above ground for the black level at the output be within -0.1V to 0.1V. In some applications, the sync tip level from the video DAC might have an offset greater than 50mV. With this input signal, the black level at the output of the MAX9503/5 might be greater than 100mV. If a ground black level is needed at the output, the circuit in Figure 1 can be used to level shift the input signal down to adjust the output black level. Assuming the driving load of the video DAC is resistor is connected between the input and CPVSS (-3.3V), the output of the negative charge 150 , a 13k pump. This resistor-divider network will level shift the input signal down by approximately 40mV. The ripple on the charge pump output is approximately 40mVP-P. Using this resistor-divider network, the ripple noise at the video input is less than 0.5mV, which is negligible.
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