CN107438215A - 无开关前置放大输入电路及其操作方法 - Google Patents

无开关前置放大输入电路及其操作方法 Download PDF

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CN107438215A
CN107438215A CN201710386382.XA CN201710386382A CN107438215A CN 107438215 A CN107438215 A CN 107438215A CN 201710386382 A CN201710386382 A CN 201710386382A CN 107438215 A CN107438215 A CN 107438215A
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impedance
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frequency apparatus
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audio frequency
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塞巴斯蒂安·德弗里斯
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Tymphany Hong Kong Ltd
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Abstract

本公开涉及无开关前置放大输入电路及其操作方法。一种无开关前置放大输入电路包括音频输入连接器，该音频输入连接器接收可以以第一阻抗操作的第一音频设备以及可以以小于第一阻抗的第二阻抗操作的第二音频设备。前置放大电路响应于放大通过第一音频设备产生的第一音频信号或者通过第二音频设备产生的第二音频信号输出前置放大的音频信号。无开关前置放大输入电路进一步包括阻抗选择器电路，该阻抗选择器电路响应于将第二音频设备连接至音频输入连接器调整输出处的阻抗以达到第二阻抗并且响应于将第一音频设备连接至音频输入调整输出处的阻抗以达到第一阻抗。

Description

无开关前置放大输入电路及其操作方法
技术领域
本公开内容涉及音频应用，并且更具体地，涉及音频放大电路。
背景技术
传统的音频放大器通常需要提供低电流DC输出或者非常昂贵的可切换的麦克风线路。此外，音频放大电路可以包括音频混合器电路，该音频混合器电路包括模拟输入级。混合器模拟输入级通常被设计成处理各种不同种类的音频输入信号。例如，混合器模拟输入级可接收高阻抗(例如，20千欧姆至2兆欧姆)线路/DI输入(line/DI input)或者低阻抗(600欧姆至3千欧姆)麦克风输入的介质。
发明内容
根据一个实施方式，提供了包括麦克风前置放大级的前置放大电路。包括直接注入(DI)单元(direct injection unit)的麦克风前置放大级在没有线路或者麦克风转换器的情况下提供高阻抗电源信号和低阻抗XLR可操作的连接。前置放大电路进一步包括偏压输入至模拟数字转换器(ADC)的自偏压输入部件(self-biasing input component)(例如，晶体管对)。以这种方式，提供低成本、强电流DC耦合的耳机输出。
根据至少一个非限制性实施方式，无开关前置放大输入电路(switchless pre-amplifier input circuit)包括音频输入连接器，该音频输入连接器接收可以以第一阻抗操作的第一音频设备以及可以以小于第一阻抗的第二阻抗操作的第二音频设备。前置放大电路(preamplifier circuit)响应于放大通过第一音频设备产生的第一音频信号或者通过第二音频设备产生的第二音频信号来输出前置放大的音频信号。无开关前置放大输入电路进一步包括阻抗选择器电路，该阻抗选择器电路响应于将第一音频设备连接至音频输入连接器来调整输出处的阻抗以达到第一阻抗并且响应于将第二音频设备连接至音频输入来调整输出处的阻抗以达到第二阻抗。
根据另一非限制性实施方式，操作无开关前置放大输入电路的方法包括在音频输入连接器处接收可以以第一阻抗操作的第一音频设备以及可以以小于第一阻抗的第二阻抗操作的第二音频设备。该方法进一步包括响应于将第一音频设备连接至音频输入连接器来调整阻抗选择器电路的输出处的阻抗以达到第一阻抗，并且响应于将第二音频设备连接至音频输入来调整输出处的阻抗以达到第二阻抗。该方法进一步包括响应于放大通过第一音频设备产生的第一音频信号或者通过第二音频设备产生的第二音频信号经由前置放大电路输出经前置放大的音频信号。
附图说明
现在结合附图和详细说明参考以下简要描述以更完整的理解本公开内容，其中，相同参考标号表示相同部件：
图1是根据非限制性实施方式的包括具有在没有线路/mic开关的情况下可操作的高阻抗DI单元和低阻抗XLR连接器的麦克风前置放大级的前置放大电路的示意图；
图2是传统的音频仪器/麦克风输入电路的示意图；
图3是根据本发明的非限制性实施方式的无开关线路DI/Mic前置放大输入电路的示意图。
具体实施方式
为了处理各种不同的输入信号(即，是高阻抗信号的一些信号和是低阻抗信号的其他信号)，传统的仪器/麦克风输入电路通常需要两个单独的前置放大器。第一前置放大器处理高阻抗信号，同时第二前置放大器处理低阻抗信号。为了选择正确的前置放大器处理进入信号，传统的模拟输入电路还执行物理的(即，机械的)单刀双掷(SPDT)开关，有时称为“Y型开关”(参见图2，开关047)。机械开关047消耗空间同时还增加仪器/麦克风输入电路的总成本。
本发明的各种非限制性实施方式提供了无开关线路DI/Mic前置放大输入电路，本文中称为提供用于连接至仪器设备或者麦克风的输入线的无开关L/M输入电路。无开关L/M输入电路响应于将麦克风设备连接至无开关L/M输入电路的输入线利用耦接至麦克风设备的电路阻抗的线路/仪器输入运算放大器(OpAmp)的虚拟的零欧姆性质。
现在参考图1，根据非限制性实施方式示出了前置放大电路100。前置放大电路100包括麦克风前置放大级102(即，电路)、PSU 104、数模转换器级106以及耳机放大级(108)。麦克风前置放大级包括在没有线路或者麦克风开关的情况下提供高阻抗电源信号和低阻抗XLR可操作的连接的直接注入(DI)单元。DI单元可将高阻抗电源信号(例如，高阻抗、线路电平、不平衡电源信号)连接至低阻抗、麦克风电平、平衡输入。XLR连接可包括将高阻抗电源信号连接至低阻抗、麦克风输入以提供平衡的音频相互连接的XLR电连接器。
根据非限制性实施方式，DI单元可在输入与输出之间提供电接地绝缘，并且它们将电源信号的阻抗与负载的阻抗匹配。例如，DI单元可利用高输入阻抗执行并且低输出阻抗可用于将输入设备(例如，吉他、贝斯等)与第二设备(例如，混合设备)的输入级匹配。在至少一个实施方式中，DI单元是接收通过PSU 104产生的幻象电源输出(phantom poweroutput)的有源电力DI单元。
前置放大电路进一步包括偏压输入至模拟数字转换器(ADC)的自偏压输入部件(例如，晶体管对)。自偏压输入部件可实现为面结型场效应晶体管(JFET)对或者运算放大器对。以这种方式，提供了低成本、强电流DC耦合的耳机输出。
现在转至图3，根据非限制性实施方式示出了无开关线路DI/Mic前置放大输入电路300(即，无开关L/M输入电路300)。无开关L/M输入电路300基于麦克风设备的连接利用耦接至麦克风设备的电路阻抗的线路/仪器输入OpAmp 035的虚拟的零欧姆性质(virtualzero-ohm nature)。在至少一个实施方式中，OpAmp 035响应于将麦克风设备连接至无开关线路DI/Mic前置放大输入电路300直接抑制穿过其中的音频信号。以这种方式，无开关L/M输入电路300在不使用物理的(即，机械的)开关或者晶体管开关的情况下可以在高阻抗仪器/线路电平输入运行状态与低阻抗麦克风输入运行状态之间转换。
无开关L/M输入电路300包括音频输入连接器032、前置放大电路302和阻抗选择器电路304。在至少一个实施方式中，音频输入连接器032是被配置为接收来自麦克风设备(未示出)的连接和/或来自线路电平设备(line-level device)或者仪器电平设备(instrumental-level device)的连接的三极立体声音频连接器(3-pole stereo audioconnector)。
前置放大电路302包括前置级OpAmp 037、幻象电源(phantom power supply)035以及分压电阻器R8和R11(由虚线圆表示)。前置级OpAmp037可以是标准的仪器放大电路或者集成电路(IC-未示出)。前置级OpAmp的增益可以通过可变电阻器(VR1)038设置。
幻象电源被配置为将DCd电力供应至DC音频设备，诸如，电容式麦克风。在至少一个实施方式中，幻象电源产生施加到音频输入连接器(即，引脚2和3)的48V dc电压。幻象电源还可以包括阻止输出的幻象电力电压(例如，48V dc)与前置级OpAmp 037的操作产生干扰的电容器034。分压电阻器R8和R11调节所输出的幻象电力电压。在至少一个实施方式中，考虑到当设置由电阻网络036(即，R1、R6、R10、R8、R11、R7、R13、R9和R12)限定的阻抗时，分压电阻器R8和R11具有固定值(例如，6.81千欧姆)。
阻抗选择器电路304包括一对输入线OpAmp 035。输入线OpAmp 035的非反相输入电耦接至音频输入连接器032。第一输入线OpAmp 035(例如，U1A)的输出连接至包括在前置放大电路304中的前置级OpAmp 037的非反相输入。第二输入线OpAmp 035(例如，U1B)的输出连接至前置级OpAmp 037的非反相输入。
当在音频输入连接器032处实现麦克风连接时，输入线OpAmp(U1A和U1B)的输入通过音频输入连接器032(即，通过连接器引脚306S至SN、R至RN、T至TN(由虚线椭圆表示))短路。连接麦克风有效激活无开关L/M输入电路300的低阻抗麦克风输入运行状态。因此，OpAmp 050(U1A和U1B)的输出由于反馈机制的性质有效地称为虚拟接地，这维持音频带中接近零欧姆的输出。麦克风输入阻抗由包括例如R1、R6、R10、R8、R11、R7、R13、R9和R12的电阻器的网络036限定。输入线OpAmp(U1A和U1B)可以出来为通过连接至输入线OpAmp(U1A和U1B)的输出的电阻器036(即，R1和R6)实现的接地连接。进一步地，输入线OpAmp(U1A和U1B)有效地用作电力虚拟接地。因此，当插入麦克风时，防止音频信号从输入线OpAmp(U1A和U1B)输出。
当在音频输入连接032处实现连接的线路电平或者仪器电平信号时，输入线OpAmp(U1A和U1B)转换为有源整体增益缓冲放大级以激活高阻抗仪器/线路电平输入运行状态。因此，输入线OpAmp(U1A和U1B)将线路输入与前置级OpAmp 037隔离，并且阻抗由包括电阻器R1、R6、R10、R8、R11、R7、R13、R9和R12的电阻网络036限定。在一个或多个实施方式中，线路电平/仪器电平阻抗通过电阻器R2、R3、R4和R5被设为高差动阻抗(例如，大约500千欧姆至大约2兆欧姆)。此外，第一电阻器组(例如，R1、R5)与第二电阻器组R10、R8、R11、R7、R13、R9和R12的组合形成给定线路电平输入所需的信号衰减的自然的分压网络。
如本文中所描述的，本公开内容的各种实施方式提供了在不使用物理的(即，机械的)开关或者晶体管开关的情况下可以在高阻抗仪器/线路电平输入运行状态与低阻抗麦克风输入运行状态之间转换的无开关线路DI/Mic前置放大输入电路。在至少一个实施方式中，无开关线路DI/Mic前置放大输入电路在不需要或者不使用物理/机械开关或者晶体管开关的情况下利用运算放大器的虚拟的零欧姆输出特性以结合两个输入级。以这种方式，无开关线路DI/Mic前置放大输入电路减少部件空间消耗和总成本。
如本文中使用的，术语“模块”是指专用集成电路(ASIC)、电子电路、微处理器、计算机处理器(共享的、专用的或者团体的)以及执行一个或多个软件或者固件程序的存储器、组合逻辑电路、包括各种输入和输出的微控制器、和/或提供所描述的功能的其他合适的部件。该模块被配置为执行各种算法、转换和/或逻辑过程以产生控制部件或者系统的一个或多个信号。当在软件中实现时，模块可以体现在作为通过处理电路(例如，微处理器)可读的非易失性机器可读存储介质并且存储通过用于执行方法的处理电路执行的指令的存储器。控制器是指包括能够存储算法、逻辑或者计算机可执行指令的存储单元的电子硬件控制器，并且包含解释和执行指令所必须的电路。
以上所要求保护的所有设备或者步骤加上功能元件的对应结构、材料、作用以及等同物旨在包括结合特定要求保护的其他要求保护元件而执行功能的任何结构、材料或者作用。为了说明和描述的目的呈现了本发明的描述，但是并不旨在以所公开的形式穷尽或限制本发明。在不背离本发明的范围和精神的情况下，许多修改和变化对本领域普通技术人员来说是显而易见的。选择和描述实施方式以对本发明的原理和实际应用进行最佳说明，并且使得本领域的其他普通技术人员能够理解本发明，具有各种修改的各种实施方式适合于预期的特定使用。
尽管已经描述了本发明的优选实施方式，然而本领域技术人员应当理解的是，现在和将来可做出属于所附权利要求的范围内的各种改善和增强。这些权利要求应被解释为保持了对首先描述的发明的适当保护。

Claims (12)

1.一种无开关前置放大输入电路，包括：
音频输入连接器，被配置为接收能够以第一阻抗操作的第一音频设备以及能够以小于所述第一阻抗的第二阻抗操作的第二音频设备；
前置放大电路，响应于放大通过所述第一音频设备产生的第一音频信号或者通过所述第二音频设备产生的第二音频信号输出经前置放大的音频信号；
阻抗选择器电路，包括与所述音频输入连接器电气通信的输入和与所述前置放大电路电气通信的输出，所述阻抗选择器电路被配置为响应于将所述第一音频设备连接至所述音频输入连接器来调整所述输出处的阻抗以达到所述第一阻抗并且响应于将所述第二音频设备连接至所述音频输入连接器来调整所述输出处的阻抗以达到所述第二阻抗。
2.根据权利要求1所述的无开关前置放大输入电路，其中，在没有机械开关的情况下调整所述输出处的阻抗。
3.根据权利要求1所述的无开关前置放大输入电路，其中，所述第一音频设备是线路电平音频设备和仪器电平音频设备中的至少一个，并且其中，所述第二音频设备是麦克风。
4.根据权利要求3所述的无开关前置放大输入电路，其中，所述第一阻抗在从约500千欧姆至约2兆欧姆的范围内，并且所述第二阻抗为约0欧姆。
5.根据权利要求1所述的无开关前置放大输入电路，其中，所述阻抗选择器电路进一步包括基于所述第一音频设备和所述第二音频设备的连接而选择性地调整所述输出处的阻抗的第一运算放大器和第二运算放大器。
6.根据权利要求5所述的无开关前置放大输入电路，其中，响应于连接所述第二音频设备，使所述第一运算放大器和所述第二运算放大器的放大输入短路，使得所述输出达到所述第二阻抗。
7.根据权利要求6所述的无开关前置放大输入电路，其中，使所述放大输入短路产生接地参考点以促使所述输出达到所述第二阻抗。
8.一种操作无开关前置放大输入电路的方法，所述方法包括：
在音频输入连接器处接收能够以第一阻抗操作的第一音频设备以及能够以小于所述第一阻抗的第二阻抗操作的第二音频设备；
响应于将所述第一音频设备连接至所述音频输入连接器来调整阻抗选择器电路的输出处的阻抗以达到所述第一阻抗并且响应于将所述第二音频设备连接至所述音频输入连接器来调整所述输出处的阻抗以达到所述第二阻抗；并且
响应于放大通过第一音频设备产生的第一音频信号或者通过第二音频设备产生的第二音频信号经由前置放大电路输出经前置放大的音频信号。
9.根据权利要求8所述的方法，其中，所述第一音频设备是线路电平音频设备和仪器电平音频设备中的至少一个，并且其中，所述第二音频设备是麦克风。
10.根据权利要求8所述的方法，进一步包括在没有操作机械开关的情况下调整所述输出处的阻抗。
11.根据权利要求8所述的方法，其中，所述第一阻抗在从约500千欧姆至约2兆欧姆的范围内，并且所述第二阻抗为约0欧姆。
12.根据权利要求8所述的方法，进一步包括响应于连接所述第二音频设备在所述音频输入连接器与所述阻抗选择器电路之间产生接地参考点以促使所述输出达到所述第二阻抗。
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