Typical Performance Characteristics Unless otherwise specified, VS = +5V, single supply,
TA = 25˚C. (Continued)
THD vs. Frequency
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added in parallel with 220 picofarads capacitance, to in-
crease the φm 20˚(approx.), but at the price of about a 100
kHz of bandwidth.
Application Note
This application note is divided into two sections: design
considerations and Application Circuits.
Overall, the LMV821/822/824 family provides good stability
for loaded condition.
DESIGN CONSIDERATIONS
This section covers the following design considerations:
1. Frequency and Phase Response Considerations
2. Unity-Gain Pulse Response Considerations
3. Input Bias Current Considerations
FREQUENCY AND PHASE RESPONSE
CONSIDERATIONS
The relationship between open-loop frequency response
and open-loop phase response determines the closed-loop
stability performance (negative feedback). The open-loop
phase response causes the feedback signal to shift towards
becoming positive feedback, thus becoming unstable. The
further the output phase angle is from the input phase angle,
the more stable the negative feedback will operate. Phase
Margin (φm) specifies this output-to-input phase relationship
at the unity-gain crossover point. Zero degrees of phase-
10012860
margin means that the input and output are completely in
phase with each other and will sustain oscillation at the
unity-gain frequency.
FIGURE 1. Phase Margin vs Common Mode Voltage for
Various Loads
The AC tables show φm for a no load condition. But φm
changes with load. The Gain and Phase margin vs Fre-
quency plots in the curve section can be used to graphically
determine the φm for various loaded conditions. To do this,
examine the phase angle portion of the plot, find the phase
margin point at the unity-gain frequency, and determine how
far this point is from zero degree of phase-margin. The larger
the phase-margin, the more stable the circuit operation.
The bandwidth is also affected by load. The graphs of Figure
1 and Figure 2 provide a quick look at how various loads
affect the φm and the bandwidth of the LMV821/822/824
family. These graphs show capacitive loads reducing both
φm and bandwidth, while resistive loads reduce the band-
width but increase the φm. Notice how a 600Ω resistor can be
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