Datasheet ADA4310-1 (Analog Devices) - 10

link to page 10
ADA4310-1 Data Sheet THEORY OF OPERATION
The ADA4310-1 is a current feedback amplifier with high Because G × RIN << RF for low gains, a current feedback output current capability. With a current feedback amplifier, the amplifier has relatively constant bandwidth vs. gain, the 3 dB current into the inverting input is the feedback signal, and the point being set when |TZ| = RF. open-loop behavior is that of a transimpedance, dVO/dIIN or TZ. Of course, for a real amplifier there are additional poles that The open-loop transimpedance is analogous to the open-loop contribute excess phase, and there is a value for RF below which voltage gain of a voltage feedback amplifier. Figure 20 shows a the amplifier is unstable. Tolerance for peaking and desired simplified model of a current feedback amplifier. Because RIN is flatness determines the optimum RF in each application. proportional to 1/gm, the equivalent voltage gain is just TZ × gm,
RF
where gm is the transconductance of the input stage. Basic analysis of the fol ower with gain circuit yields
RG
V T (s)
RIN
O Z = G ×
I TZ VOUT
V T (s) + × +
IN
IN Z G RIN F R
RN
where:
VIN
017 RF G =1+ 06027- Figure 20. Simplified Block Diagram G R 1 R = ≈ IN 50 Ω gm Rev. C | Page 10 of 14 Document Outline FEATURES APPLICATIONS PIN CONFIGURATIONS GENERAL DESCRIPTION REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Maximum Power Dissipation ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION APPLICATIONS INFORMATION FEEDBACK RESISTOR SELECTION POWER CONTROL MODES OF OPERATION EXPOSED THERMAL PAD CONNECTIONS POWER LINE APPLICATION BOARD LAYOUT POWER SUPPLY BYPASSING OUTLINE DIMENSIONS ORDERING GUIDE