CN1187893C - 具有共模反馈电路的多级差分放大器 - Google Patents

具有共模反馈电路的多级差分放大器 Download PDF

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Publication number
CN1187893C
CN1187893C CN02141886.1A CN02141886A CN1187893C CN 1187893 C CN1187893 C CN 1187893C CN 02141886 A CN02141886 A CN 02141886A CN 1187893 C CN1187893 C CN 1187893C
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differential amplifier
output
load
transistor
stage
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CN1404218A (zh
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埃尔詹·拉马赞
里夏德·加焦
弗雷德里克·佩右
克里斯蒂安·施兰茨
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Intel Germany Holding GmbH
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Infineon Technologies AG
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/45—Differential amplifiers
    • H03F3/45071—Differential amplifiers with semiconductor devices only
    • H03F3/45479—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection
    • H03F3/45632—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection in differential amplifiers with FET transistors as the active amplifying circuit
    • H03F3/45636—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection in differential amplifiers with FET transistors as the active amplifying circuit by using feedback means
    • H03F3/45641—Measuring at the loading circuit of the differential amplifier
    • H03F3/45659—Controlling the loading circuit of the differential amplifier
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/45—Differential amplifiers
    • H03F3/45071—Differential amplifiers with semiconductor devices only
    • H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
    • H03F3/45179—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using MOSFET transistors as the active amplifying circuit
    • H03F3/45183—Long tailed pairs
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
    • H03F2203/45—Indexing scheme relating to differential amplifiers
    • H03F2203/45514—Indexing scheme relating to differential amplifiers the FBC comprising one or more switched capacitors, and being coupled between the LC and the IC

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)

Abstract

本发明涉及多级差分放大器，有输入级(MP1，MP2)，其中存在差分输入电压，有连接输入级(MP1，MP2)的负载(MN2，MN3)，有CMFB电路(2)和输出级(MN3，MN4)，其中放大的差分输出电压被输出。为了改进共模调节回路(1)的稳定性，增加电流源(ib3)，附加供给电流到调节回路(1)，从而保证负载(MN2，MN3)的控制电压不降到低于预定的值。

Description

具有共模反馈电路的多级差分放大器
技术领域
本发明涉及多级差分放大器，特别是有偶数级的共模反馈电路CMFB。
背景技术
运算放大器是许多应用的模拟信号处理系统的基本元件。在许多应用中，使用完全的差分运算放大器(差分放大器)的优点是，在特殊范围内输出电压不依靠共模电压。
完全差分的差分放大器一般要求CMFB电路(共模反馈电路)，用于设置共模电压，其通常位于正负电源电压之间(VDD+VSS)/2。
 具有CMFB电路的差分放大器的基本结构显示在图1中。图1显示运算放大器3有两个输入，在该输入端有差分输入电压Vindiff，有两个输出，在该输出端差分输出电压Voutdiff被输出。差分放大器3还包括CMFB电路2，该电路与输出端并联，用于调节共模电压到电源电压之间的平均值。为了这个目的，运算放大器3有附加的输入Incntr1，输出电压Uoutp，Uoutn经CMFB电路2反馈。
单级差分放大器的增益是有限的。为了更高的增益使用2级或多级差分放大器。
在美国No，5,955,922专利中描述了两级差分放大器的典型实例，其中，差分放大器的CMFB电路包括附加的逆变单元，结果，在设置共模电压的反馈回路中，反馈输入和输出间共发生三次逆变。因而反馈是稳定的。使用偶数逆变，产生正反馈，结果系统不稳定。(在这种连接中，当输入增加或控制电压导致输出量减小，使用术语逆变)。美国专利说明书图3描述的差分放大器有缺点，所以相当不稳定。
发明内容
因此，本发明的目的是改进多级，尤其是两级差分放大器的稳定性特性。
为实现上述目的，一种多级差分放大器，包括：
输入级；
负载与输入级连接；
输出级，其特征在于
反馈回路和CMFB电路，用于设置共模电压；
逆变单元连接到CMFB电路；
转换器连接到逆变单元的下游；
其中，电流源附加地供给电流进入反馈回路，以防止负载断开。
本发明的基本观念包括提供附加的电流源，电流源馈送电流到差分放大器的反馈回路，并保证足够高的电压呈现在有源负载的控制输入端，并且不切断和使后者过激励。可控制的负载绝不进入阻塞或线性状态，差分放大器仍保留功能。
按照本发明的优选实施例，在CMFB电路和输入级负载之间布置了逆变单元。在这种情况下，附加的电流源与逆变单元并联。结果，被调节的电流减小，同时，产生较小的回路增益。同时导致了差分放大器的较高稳定性，其反映在更高阶段的余数中。
按照本发明的优选实施例，还提供了I/U交换器，其连接到负载的控制节点。
逆变单元最好是晶体管，尤其象MOS(金属氧化半导体)晶体管。
按照本发明的优选实施例，输入级负载象电流反射镜一样实现，尤其象MOS电流反射镜。
输入级的输出最好连接到输出级的控制输入端(栅级)。
CMFB电路最好是SC电路(SC：开关电容器)。
附图说明
本发明参考附图通过实例详细说明，其中：
图1显示有CMFB的差分放大器的基本电路图，和
图2显示按照本发明的优选实施例的差分放大器的简化电路图。
具体实施方式
关于图1在介绍的描述中已做了说明。
图2显示差分放大器的电路图，有输入级MP1，MP2和输出级MN4，MN5。差分放大器放大在输入inn、inp处的差分信号，在输出OUTp、OUTn处输出放大的输出信号。输入级包括两个PMOS晶体管MP1，MP2，而输出级通过两个NMOS晶体管MN4，MN5实现。
输入级负载由包括晶体管MN2，MN3的单个MOS电流反射镜实现。
输入级由电流源ib1馈电，输出级由相同的电流源ib2馈电，每个MOS晶体管MN4和MN5分别连接一个电流源ib2.
差分放大器还包括带有常规CMFB电路2的反馈回路1。在每种情况下，CMFB电路2包括与输出级的每个晶体管MN4和MN5各自并联的两个电容C1n，C2n和C1p和C2p。
电容C1n，C2n，C1p，C2p的一端连接到参考电压Vref，Vref代表共模电压Vcm的理想值。电容C1n，C2n，C1p，C2p的另一端连接到电压Vbisa。电容C1n，C2n，C1p，C2p通过开关S充电或放电。
反馈回路1还包括逆变单元，在现在的情况下为PMOS晶体管MP3。晶体管MP3的栅级电压的增加带来漏电流的减少，换言之，发生负反馈或逆变。逆变单元MP3的栅级连接到CMFB电路2的输出，CMFB电路2输出控制电压Vcntr1。
作为二极管连接的NMOS晶体管MN1连接到逆变单元MP3的漏端。所述晶体管MN1的栅极连接到电流反射镜MN2，MN3的栅极。作为二极管连接的晶体管MN1基本上作为I/U转换器，用于为电流反射镜MN2，MN3提供控制电压。
晶体管MN2，MN3的漏极被反馈到输出级各自的晶体管MN4和MN5的栅极。
上述的结构已经发挥功能，但是在逆变单元MP3的高控制电压Vcntr1可能有稳定的问题。象提到的那样，晶体管MP3的漏电流在高控制电压Vcntr1减少。在非常小的电流的情况下，因而可能发生晶体管MN1获得高阻抗，负载的晶体管MN2，MN3断开。
为了避免出现这样的问题，增加了电流源ib3，它与逆变单元MP3并联，也就是供电压Vdd和变换单元MP3的输出。电流源ib3补充供给电流进入反馈回路1，因而保证足够的电流以保持晶体管MN1和负载MN2，MN3在接通状态。电流源ib3供给的电流尤其确保晶体管MN1的电压高于晶体管MN1阈值电压。
如果控制电压Vcntr1趋向Vss，负载MN2，MN3的控制电压不趋向电流源电压VDD，这是因为电流源ib3的原因。因而输入级MP1，MP2永不断开。由于调节电路增益因子的减少，在低速进行校正是有效的，从而整体上实现了较大的稳定性。

Claims (9)

1.一种多级差分放大器，包括：
输入级(MP1，MP2)；
负载(MN2，MN3)与输入级(MP1，MP2)连接；
输出级(MN4，MN5)，其特征在于
反馈回路(1)和CMFB电路(2)，用于设置共模电压；
逆变单元(MP3)连接到CMFB电路(2)；
转换器(MN1)连接到逆变单元(MP3)的下游；
其中，电流源(ib3)附加地供给电流进入反馈回路(1)，以防止负载(MN2，MN3)断开。
2.据权利要求1所述多级差分放大器，其特征在于：
I/U转换器是包括源极、漏极和栅极的晶体管(MN1)，所述栅极连接到漏极。
3.根据权利要求1所述多级差分放大器，其特征在于：
逆变单元(MP3)是晶体管，特别是PMOS晶体管。
4.根据权利要求1所述多级差分放大器，其特征在于：
负载(MN2，MN3)是电流反射镜。
5.根据权利要求4所述多级差分放大器，其特征在于：
I/U转换器连接到负载(MN2，MN3)。
6.根据权利要求1所述多级差分放大器，其特征在于：
CMFB电路(2)由SC电路形成。
7.根据权利要求1所述多级差分放大器，其特征在于：
输入级(MP1，MP2)的输出连接到输出级(MN4，MN5)的控制输入。
8.根据权利要求1所述多级差分放大器，其特征在于：
电流源(ib3)与逆变单元(MP3)并联连接。
9.根据权利要求1所述多级差分放大器，其特征在于：
差分放大器的级的数目是偶数，特别是2。
CN02141886.1A 2001-08-31 2002-08-27 具有共模反馈电路的多级差分放大器 Expired - Fee Related CN1187893C (zh)

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DE10142707A DE10142707A1 (de) 2001-08-31 2001-08-31 Mehrstufiger Differenzverstärker mit CMFB-Schaltkreis
DE10142707.7 2001-08-31

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DE10142707A1 (de) 2003-04-03
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US20030048134A1 (en) 2003-03-13

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