Datasheet > AB-193

AB-193

更新时间： 2024-10-13 23:26:55

品牌	Logo	应用领域
其他 - ETC		运算放大器
页数	文件大小	规格书
12页	124K
描述
AB-193 - THE CURRENT-FEEDBACK OP AMP A HIGH-SPEED BUILDING BLOCK

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AB-193 数据手册

AP P LICATION BULLETIN

Mailing Address: PO Box 11400 • Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd. • Tucson, AZ 85706

Tel: (602) 746-1111 • Twx: 910-952-111 • Telex: 066-6491 • FAX (602) 889-1510 • Immediate Product Info: (800) 548-6132

THE CURRENT-FEEDBACK OP AMP

A HIGH-SPEED BUILDING BLOCK

By Anthony D. Wang, Burr-Brown Corp.

Although current-feedback amplifiers (CFAs) have been in

the evolution of the beast, it helps to look back to some early

discrete transistor circuits.

use for quite some time, there is a reluctance to view them

in the same light as voltage-feedback amplifiers (VFAs). For

instance, the gain-bandwidth curve of VFAs has a parallel

in a transimpedance-bandwidth curve for CFAs. This pa-

rameter can be used to determine the closed-loop behavior

of the CFA in the same way that GBW can for the VFA. Not

all the fault is with the users—the amplifier manufacturers

have not standardized the CFA characterization as they

have done with VFAs. This paper describes the CFA and its

behavior in an intuitive manner.

The three transistor amplifier of Figure 1 is arranged in a

series-shunt configuration. However, in order to analyze the

amplifier, the circuit is rearranged as shown in Figure 2.

The feedback network shows up in two places—a series

network at the output and a parallel network at the emitter of

the input transistor. This allows for open-loop analysis while

keeping the effects of loading intact.

The loading of the output by the feedback network is

generally not a problem. However, the gain of the first

transistor stage is dependent on the values of the resistors in

the feedback network. Thus the open-loop response will

change with closed-loop gain (as the feedback network

changes), which could make frequency compensation an

iterative chore.

HISTORICAL PERSPECTIVE

The term “operational amplifier,” or “op amp” in typical

engineering shorthand, has generally been associated with

the transistorized voltage-feedback amplifier. It is becoming

more acceptable now to include the current-feedback ampli-

fier in the same category.

The discrete transistor circuit of Figure 3 circumvents this

difficulty. Adding another transistor, Q₄, to buffer the input

stage transistor, Q₁, from the feedback network illustrates

this modification. This is the first step to a voltage feedback

amplifier topology.

Interestingly enough, the basic architecture for the CFA

might have predated the VFA although it was not until the

1980s that the CFA was itself repopularized. To appreciate

R₁

R₂

R₁

R₂

Q₂

C_T

V_IN

Q₁

Q₃

R_F

V_OUT

_F• R_G

R_G

R₃

R_E

R₃

R_L= R_F+ R_G

R_F+ R_G

FIGURE 1. Three Transistor Amplifier.

FIGURE 2. Amplifier Redrawn for Analysis.

AB-193

12 3 4 5 6 7...12

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与AB-193相关器件

型号	品牌	获取价格	描述	数据表
AB-194	ETC	获取价格	AB-194 - INTERMODULATION DISTORTION (IMD)
AB1A3M	NEC	获取价格	on-chip resistor NPN silicon epitaxial transistor
AB1A3M	RENESAS	获取价格	700mA, 25V, NPN, Si, SMALL SIGNAL TRANSISTOR, TO-92, SC-43B, 3 PIN
AB1A4A	NEC	获取价格	on-chip resistor NPN silicon epitaxial transistor
AB1A4A	RENESAS	获取价格	700mA, 25V, NPN, Si, SMALL SIGNAL TRANSISTOR, TO-92, SC-43B, 3 PIN
AB1A4M	NEC	获取价格	on-chip resistor NPN silicon epitaxial transistor
AB1F3P	NEC	获取价格	on-chip resistor NPN silicon epitaxial transistor
AB1F3P	RENESAS	获取价格	700mA, 25V, NPN, Si, SMALL SIGNAL TRANSISTOR, TO-92, SC-43B, 3 PIN
AB1F3P-AZ	NEC	获取价格	Small Signal Bipolar Transistor, 0.7A I(C), 25V V(BR)CEO, 1-Element, NPN, Silicon, TO-92,
AB1J3P	NEC	获取价格	on-chip resistor NPN silicon epitaxial transistor

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