Hi,
In your BUF802 datasheet, there is an attachment of typical application, the scope front-end amplifier design figure 9-1. For I understand, the design is to trying to give a 1Mohm input R circuit. There is not much information regarding input capacitance. Input capacitance/resistance is important to me, should you have any reference design to optimize input R and C? Look forward to your reply, many thanks.
Y
Hello,
For internal input impedance of the BUF802, this can be found under Input specifications of the datasheet:
Also, there is a plot of input impedance over frequency under Figure 6-21. Keep in mind your signal will see an impedance of the 50gohm // cap impedance. This information can be used in relation to your input impedance to the device over frequency. BUF802's giga ohms of input impedance was tested against a total input impedance of both 1MOhm and 50Ohm. This impedance can be calculated as a total of your capacitance + resistance at your signal frequency. And, if optimization for performance is necessary via impedance matching, this can be found under S11 Optimization on page 23 in the datasheet.
Stability wise, depending on your configuration, your input capacitance will interact with your surrounding resistor values which may require compensation via inclusion of feedback capacitance. Pole/zero calculation can be found on page 23-24 under Uniform Gain Across Frequency section.
Thank you,
Sima
