JP3809716B2 - Voltage-current conversion circuit - Google Patents

Description

…（４）
【００３２】
また、カレントミラー回路ＩＳＣ２の電流値をｉ_cs2 とし、出力電流をｉ_out とすると、トランジスタＱ４のコレクタ電流ｉ_c4は（ｉ_out ＋ｉ_cs2 ）となる。即ち、（ｉ_c3＝ｉ_cs2 ＝ｉ_c4−ｉ_out ）である。電流源ＩＳ２の電流値をｉ₂ とすると、次の式が得られる。
【００３３】
【数５】
ｉ₂ ＝ｉ_c3＋ｉ_c4＝２ｉ_c4−ｉ_out
ｉ_c4＝（ｉ₂ ＋ｉ_out ）／２ …（５）
【００３４】
さらに、トランジスタＱ３のコレクタ電流ｉ_c3は、次式により求まる。
【００３５】
【数６】
ｉ_c3＝ｉ₂ −ｉ_c4＝（ｉ₂ −ｉ_out ）／２ …（６）
【００３６】
ここで、トランジスタＱ３およびＱ４の飽和電圧をそれぞれｉ_s3，ｉ_s4とすると、トランジスタＱ３とＱ４のベース・エミッタ間電圧Ｖ_be3 ，Ｖ_be4 はそれぞれＶ_t ｌｎ（ｉ_c3／ｉ_s3）およびＶ_t ｌｎ（ｉ_c4／ｉ_s4）で表されるので、次式が得られる。
【００３７】
【数７】

…（７）
【００３８】
図示のように、トランジスタＱ１のベース電圧をＶ１とし、トランジスタＱ２またはトランジスタＱ３のベース電圧をＶ２とすると、次式が得られる。
【００３９】
【数８】
Ｖ１−Ｖ_be1 ＝Ｖ２−Ｖ_be2
Ｖ１−Ｖ２＝Ｖ_be1 −Ｖ_be2 …（８）
【００４０】
【数９】
Ｖ２−Ｖ_be3 ＝Ｖ１−Ｖ_be4
Ｖ１−Ｖ２＝Ｖ_be4 −Ｖ_be3 …（９）
【００４１】
ここで、トランジスタＱ１，Ｑ２，Ｑ３およびＱ４は、同一の電気特性を有するものを用いているとすると、これらのトランジスタの飽和電流ｉ_s1，ｉ_s2，ｉ_s3，ｉ_s4は同一の値である。
【００４２】
式（８）および式（９）により、次式が得られる。
【００４３】
【数１０】
Ｖ_be1 −Ｖ_be2 ＝Ｖ_be4 −Ｖ_be3 …（１０）
【００４４】
式（４）および（７）を式（１０）に代入すると、次式が得られる。
【００４５】
【数１１】
（ｉ₁ ＋ｉ_in）／（ｉ₁ −ｉ_in）＝
（ｉ₂ ＋ｉ_out ）／（ｉ₂ −ｉ_out ）
ｉ_out ＝ｉ_in・ｉ₂ ／ｉ₁ …（１１）
【００４６】
ここで、（ｉ₁ ＝ｉ₂ ）、即ち、電流源ＩＳ１とＩＳ２の電流値が等しいとすると、（ｉ_out ＝ｉ_in）となる。
差動増幅回路ＡＭＰ４において、出力抵抗素子Ｒ３の抵抗値をｒ３とすると、（Ｖ_out ＝ｉ_out ・ｒ３）となる。
【００４７】
さらに、入力抵抗素子Ｒ２と出力抵抗素子Ｒ３の抵抗値が同じであるとすると、入力信号Ｖ_inの変化量ΔＶ_inに応じて、出力信号Ｖ_out に生じた変化量ΔＶ_out はΔＶ_inと等しい。即ち、（ΔＶ_out ＝ΔＶ_in）である。
【００４８】
上述のように、入力信号Ｖ_inが図２（ａ）に示すように、直流成分Ｖ_DCを持った信号として入力されると、抵抗素子Ｒ１とキャパシタＣ１で構成されたローパスフィルタにより直流成分Ｖ_DCが抽出される。抽出した直流成分Ｖ_DCは差動増幅回路ＡＭＰ３に入力され、それに応じた電圧Ｖ２が差動増幅回路ＡＭＰ１，ＡＭＰ２のトランジスタＱ２，Ｑ３のベースにそれぞれ印加される。即ち、直流成分Ｖ_DCに応じて発生した電圧Ｖ２が差動増幅回路ＡＭＰ１のマイナス入力側に帰還されることにより、差動増幅回路ＡＭＰ３のトランジスタＱ５とＱ６のベースがイマジナリーショートされ、電圧Ｖ１と直流成分Ｖ_DCが等しくなる。これによって、出力電流ｉ_out に入力信号Ｖ_inの直流成分Ｖ_DCを含まず、純粋に交流成分のみが転送される。
【００４９】
また、差動増幅回路ＡＭＰ３で差動増幅回路ＡＭＰ１のマイナス側に直流成分Ｖ_DCを帰還させて、それを抑えることにより、差動増幅回路ＡＭＰ１において、ダイオード接続となるトランジスタＱ１のエミッタ抵抗ｒ_e が入力インピーダンスに現れることなく、入力端子からみた入力インピーダンスは、純粋に入力抵抗Ｒ２のみとなるため、回路のリニア特性がよく、信号の歪みを低減することができる。
【００５０】
以上説明したように、本実施形態によれば、抵抗素子Ｒ１とキャパシタＣ１で構成したローパスフィルタにより、入力信号Ｖ_inの直流成分Ｖ_DCを抽出し、差動増幅回路ＡＭＰ３に入力し、それに応じた電圧Ｖ２を差動増幅回路ＡＭＰ３により発生し、差動増幅回路ＡＭＰ１のマイナス入力側に帰還することで、差動増幅回路ＡＭＰ１のトランジスタＱ１のベースは直流成分Ｖ_DCと同電位に保持する。また、トランジスタＱ１のベースに、入力抵抗素子Ｒ２を介して入力信号Ｖ_inを印加するので、入力信号Ｖ_inとその直流成分Ｖ_DCとの差分信号が生成され、差動増幅回路ＡＭＰ２により、当該差分信号に応じた出力電流ｉ_out を発生するので、電流ｉ_out は直流成分Ｖ_DCを含まず、入力信号の振幅のみに依存する。
これによって、回路のリニア特性が改善され、信号の歪みが低減することができ、且つ直流成分を抽出するローパスフィルタの抵抗素子を大きくすることができるため、ＩＣチップの外部に接続されるキャパシタの容量を小さくで済み、外付け部品のコスト削減を実現可能である。また、オフセットをキャンセルするため電流源を折り返し使用することなく、低電源電圧動作を実現可能である。
【００５１】
第２実施形態
図３は本発明に係る電圧−電流変換回路の第２の実施形態を示す回路図である。
図示のように、本実施形態の電圧−電流変換回路は、図１に示す本発明の第１の実施形態に較べて、差動増幅回路ＡＭＰ１の構成が異なり、それ以外の部分はすべて同じである。図３では、図１と同じ回路素子および同じ構成を有する回路部分は、同じ符号を付して表記する。
【００５２】
本実施形態では、差動増幅回路ＡＭＰ１において、トランジスタＱ１とＱ２のエミッタ同士の接続点に、可変電流源ＩＳＶ１が接続されている。可変電流源ＩＳＶ１の供給電流を制御することにより、出力信号Ｖ_out のレベルを調整することができる。
【００５３】
上述した式（１１）により、電流源ＩＳ１またはＩＳ２の何れかの電流値ｉ₁ またはｉ₂ を制御することで、出力信号Ｖ_out の変化量ΔＶ_out を調整できる。このため、図３に示すように、入力信号Ｖ_inの変化量ΔＶ_inが一定で、即ち、ｉ_inが一定の場合に、可変電流源ＩＳＶ１の電流を大きく設定すれば、出力信号Ｖ_out の変化量ΔＶ_out が小さくなり、逆に変換電流源ＩＳＶ１の電流を小さく設定すれば、出力信号の変化量ΔＶ_out が大きくなる。
【００５４】
このように、差動増幅回路ＡＭＰ１に供給する電流値を制御することにより、出力信号のレベルを制御でき、例えば、音量を調整する電子ボリュームを実現可能である。
【００５５】
以上説明したように、本実施形態によれば、差動増幅回路ＡＭＰ１に可変電流源ＩＳＶ１により駆動電流を供給し、当該可変電流源をＩＳＶ１の電流を制御することにより、出力信号の振幅を制御することができ、電子ボリュームを実現できる。
なお、出力信号の振幅制御は、差動増幅回路ＡＭＰ１の駆動電流源に限らず、差動増幅回路ＡＭＰ２の駆動電流源の電流を制御することによっても実現できる。
【００５６】
第３実施形態
図４は本発明に係る電圧−電流変換回路の第３の実施形態を示す回路図である。
図示のように、本実施形態では上述した第２の実施形態に較べて、差動増幅回路ＡＭＰ２にトランジスタＱ７が新たに設けられている。
トランジスタＱ７のコレクタが電源電圧Ｖ_CCに接続され、ベースが可変電圧源ＶＳ２に接続され、エミッタがトランジスタＱ３とＱ４のエミッタ同士の接続点に接続されている。
【００５７】
図４に示す構成を有する電圧−電流変換回路において、差動増幅回路ＡＭＰ１の可変電流源ＩＳＶ１の電流を制御することにより、出力信号Ｖ_out の振幅を制御することができる。即ち、出力信号のボリューム調整ができる。さらに、可変電圧源ＶＳ２の電圧値ｖ３を制御することにより、出力信号Ｖ_out の振幅を０に保持する、いわゆるミュート（Ｍｕｔｅ）機能を実現できる。
【００５８】
差動増幅回路ＡＭＰ２において、トランジスタＱ３のベース電圧はＶ２である。なお、前述したように、電圧Ｖ２は入力信号Ｖ_inの直流成分Ｖ_DCと等しくなる。可変電圧源ＶＳ２の電圧値Ｖ３を調整し、Ｖ２より高く設定すると、トランジスタＱ７がオン状態となり、トランジスタＱ７のエミッタに、電流源ＩＳ２の電流値ｉ₂ と同じ電流ｉ₇ が流れる。このため、出力電流ｉ_out が０となる。これに応じて差動増幅回路ＡＭＰ４の出力信号Ｖ_out の振幅も０に保持される。
【００５９】
以上説明したように、本実施形態によれば、差動増幅回路ＡＭＰ２にトランジスタＱ７を設けて、当該トランジスタＱ７のエミッタをトランジスタＱ３とＱ４のエミッタ同士に接続し、トランジスタＱ７のベースに印加される電圧Ｖ３のレベルを制御し、トランジスタＱ７のオン／オフ状態を制御することによって、ミュート機能を実現できる。
なお、可変電圧源ＶＳ２の代わりに入力信号Ｖ_inの直流成分Ｖ_DCより電圧値が高い電圧Ｖ３を供給する固定電圧源を設けて、トランジスタＱ７のベースと当該固定電圧源との間に、スイッチを設けて、スイッチのオン／オフ状態を制御することによって、同じくミュート機能を実現できることはいうまでもない。
【００６０】
第４実施形態
図５は本発明に係る電圧−電流変換回路の第４の実施形態を示す回路図である。
図示のように、本実施形態の電圧−電流変換回路は、図１に示す第１の実施形態に較べて、差動増幅回路ＡＭＰ５と差動増幅回路ＡＭＰ６が新たに設けられている。
【００６１】
差動増幅回路ＡＭＰ５は、トランジスタＱ８，Ｑ９、電流源ＩＳ４およびカレントミラー回路ＩＳＣ４により構成されている。図示のように、差動増幅回路ＡＭＰ５は、差動増幅回路ＡＭＰ２と並列に設けられている。即ち、トランジスタＱ８のベースは、トランジスタＱ３のベースに接続され、トランジスタＱ９のベースは、トランジスタＱ４のベースに接続されている。トランジスタＱ８とＱ９のエミッタ同士が接続され、接続点が電流源ＩＳ４に接続されている。さらにトランジスタＱ８とＱ９のコレクタがダイナミック負荷を構成するカレントミラー回路ＩＳＣ４に接続されている。
【００６２】
差動増幅回路ＡＭＰ６の反転入力端子（−）は差動増幅回路ＡＭＰ５のトランジスタＱ９のコレクタに接続され、入力端子（＋）は抵抗素子Ｒ６の一方の端子に接続され、抵抗素子Ｒ６の他方の端子が電圧源ＶＳ３に接続されている。
【００６３】
ここで、例えば、差動増幅回路ＡＭＰ５を構成するトランジスタＱ８およびＱ９は、他の差動増幅回路ＡＭＰ１，ＡＭＰ２を構成するトランジスタＱ１〜Ｑ４と同一の電気特性を有する場合に、差動増幅回路ＡＭＰ５により、出力電流ｉ_out2が得られる。なお、（ｉ_out2＝ｉ_out1）となる。
【００６４】
このため、例えば、電圧源ＶＳ３の電圧値を電圧源ＶＳ１と異なるように設定することにより、出力信号Ｖ_out1と異なるオフセットを持つ出力信号Ｖ_out2を獲得できる。このように、一つの入力信号Ｖ_inから、複数の出力電圧を得ることができる。必要に応じて、これらの複数の出力信号のオフセットがそれぞれ異なる値に設定可能である。
【００６５】
以上説明したように、本実施形態によれば、差動増幅回路ＡＭＰ２と並列に差動増幅回路ＡＭＰ５を設けて、さらにその出力側に差動増幅回路ＡＭＰ６を設けることによって、入力信号Ｖ_inに応じて複数の出力電流を発生することができ、これらの出力電流に応じて、オフセットの異なる複数の出力電圧を発生できる。
【００６６】
【発明の効果】
以上説明したように、本発明の電圧−電流変換回路によれば、入力信号の直流成分を抽出し、差動増幅回路に供給することで、当該直流成分に応じた電圧を発生し、他の差動増幅回路の反転入力側に帰還することにより、入力信号の直流成分をキャンセルすることができる。また、入力信号の直流成分を抽出するローパスフィルタの抵抗素子を大きく設定できるので、キャパシタの容量を小さくでき、外付け部品のコスト削減を実現できる利点がある。
さらに、入力信号の直流成分に応じて電圧を直流成分をキャンセルする差動増幅回路の反転入力側に帰還することによって、回路の入力インピーダンスのリニア特性がよく、信号歪みの低減を実現できる。また、本発明によれば、低電圧、低消費電力の電圧−電流変換回路を実現可能である。
【図面の簡単な説明】
【図１】本発明に係る電圧−電流変換回路の第１の実施形態を示す回路図である。
【図２】第１の実施形態の入出力信号の波形を示す波形図である。
【図３】本発明に係る電圧−電流変換回路の第２の実施形態を示す回路図である。
【図４】本発明に係る電圧−電流変換回路の第３の実施形態を示す回路図である。
【図５】本発明に係る電圧−電流変換回路の第４の実施形態を示す回路図である。
【図６】従来の電圧−電流変換回路の一例を示す回路図である。
【符号の説明】
ＡＭＰ１，ＡＭＰ２，ＡＭＰ３，ＡＭＰ４，ＡＭＰ５，ＡＭＰ６…差動増幅回路、ＩＳ１，ＩＳ２，ＩＳ３，ＩＳ４…電流源、ＶＳ１，ＶＳ２，ＶＳ３…電圧源、Ｒ１，Ｒ２，Ｒ３，Ｒ４，Ｒ５，Ｒ６…抵抗素子、Ｃ１…キャパシタ、ＩＳＣ１，ＩＳＣ２，ＩＳＣ３，ＩＳＣ４…カレントミラー回路、Ｔ_C …キャパシタ接続端子、Ｖ_CC…電源電圧、ＧＮＤ…接地電位。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a voltage-current conversion circuit, and more particularly to a voltage-current conversion circuit having good linear characteristics of input / output signals and capable of operating even at a low voltage.
[0002]
[Prior art]
In an amplifier intended for an audio signal, for example, an amplifier built in a stereo IC, a current signal corresponding to the input signal is used to remove a DC component (hereinafter also referred to as offset) of the input signal or convert it to another level. A voltage-current conversion circuit for generating FIG. 6 shows an example of a generally used voltage-current conversion circuit.
[0003]
As shown in FIG. 6, the voltage-current conversion circuit of this example includes a low-pass filter constituted by a resistor element R1 and a capacitor C1, and a differential amplifier circuit constituted by transistors Q1 and Q2 and resistor element R2 current sources IS1 and IS2. It is configured.
The low-pass filter extracts the DC component V _DC of the input signal V _in and inputs it to the base of the transistor Q2. Since the input signal V _in is input to the base of the transistor Q1, the resistor R2 connected between the emitters of the transistors Q1 and Q2, corresponding to the difference between the input signal V _in and its DC component V _DC current Δi ₁ flows.
[0004]
In the differential amplifier circuit, when the current values of the current sources IS1 and IS2 are both i ₁ , a current (i ₁ + Δi ₁ ) flows through the current mirror circuits ISC01 and ISC02, and a current (i ₁₋ Δi ₁ ) flows. Since the current (i ₁ −Δi ₁ ) similarly flows through the current mirror circuits ISC21 and ISC22, an output current of 2Δi ₁ is obtained on the output side of the circuit. As described above, the current .DELTA.i ₁ flowing through the resistor R2 is proportional to the difference between the input signal V _in and the DC component V _DC. That is, the DC component V _DC of the input signal V _in is removed signal.
[0005]
As shown in FIG. 6, an output voltage _Vout represented by the following equation can be obtained by a circuit configured by connecting a resistor element R3 and a voltage source VS1 in series on the output side of the voltage-current conversion circuit.
[0006]
[Expression 1]
V _out = 2Δi ₁ · r3 + v ₁ (1)
[0007]
Here, r3 the resistance value of the resistance element R3, v ₁ is the voltage value of the voltage source VS1. Thus, the input signal V _in is converted to a voltage v ₁ to a new voltage signal V _out to offset.
[0008]
With the voltage-current conversion circuit shown in FIG. 6, it is possible to remove the DC component contained in the input signal and easily convert the offset to a desired level.
[0009]
[Problems to be solved by the invention]
However, conventional voltage mentioned above - in the current conversion circuit, the dynamic range of the input signal V _in is determined the value of the resistance element R2 and the current source IS1, IS2. Here, when the resistance value of the resistance element R2 and r _2, the dynamic range of the input signal V _in is required to be set to normal (r ₂ · i ₁₎ or more. In fact, since the emitter resistance element r _e of the transistor Q1, Q2 appears, at design time, since taking more than twice the margin required signal, the current value of the current source IS1, IS2 increases. Further, due to the influence of the emitter resistance of the transistors constituting the differential amplifier circuit, there is a disadvantage that the relationship between the input amplitude and the output amplitude becomes non-linear and distortion increases.
[0010]
Further, in the conventional voltage-current conversion circuit shown in FIG. 6, since the DC component V _DC is removed, that is, offset cancellation is performed using the folding of the current source, the low power supply voltage or the low early voltage of the pnp transistor is reduced. When the process is used, every time the signal component fluctuates due to the load resistance of the output, the collector-emitter voltage V _{CE of the} current mirror circuit composed of the pnp transistor fluctuates, and there is a disadvantage that the signal distortion increases.
[0011]
The present invention has been made in view of such circumstances, and an object of the present invention is to perform voltage-current conversion that can maintain the linear characteristic of the amplitude of the input / output signal and can operate at a low power supply voltage while suppressing the occurrence of signal distortion. It is to provide a circuit.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a voltage-current conversion circuit according to the present invention is a voltage-current conversion circuit that outputs a current signal corresponding to the amplitude of an input signal whose level fluctuates up and down around a predetermined DC component. A DC component extraction circuit for extracting a DC component of the input signal; a first differential for inputting the extracted DC component to a non-inverting input terminal and outputting a voltage signal from the output terminal according to the DC component; An amplifier circuit and an inverting input terminal are connected to the input terminal of the input signal via a resistance element, the output signal of the first differential amplifier circuit is applied to the non-inverting input terminal, and the output terminal is inverted. The second differential amplifier circuit connected to the input terminal and the output signal of the first differential amplifier circuit are input to one input terminal, and the output signal of the second differential amplifier circuit is input to the first differential amplifier circuit . 1 with the inverting input terminal of the differential amplifier circuit Input to the other input terminal, and a third differential amplifier circuit which outputs a current signal corresponding to the difference between said input signal and its DC component.
[0013]
In the present invention, it is preferable that the DC component extraction circuit is composed of a low-pass filter having a cut-off frequency set according to the frequency of the input signal.
[0014]
In the present invention, it is preferable that the second differential amplifier circuit has a base connected to an input terminal of the input signal via the resistor element, and a collector output of the second differential amplifier circuit. A first transistor forming a terminal; a second transistor whose base is connected to the output terminal of the first differential amplifier circuit; and a predetermined connection point between the emitters of the first and second transistors. The third differential amplifier circuit includes a third transistor having a base connected to the output terminal of the first differential amplifier circuit, and a base. Is connected to the output terminal of the second differential amplifier circuit, and a predetermined point is connected to a connection point between the fourth transistor to which the current signal is supplied from the collector and the emitters of the third and fourth transistors. Second current source for supplying current And the base of the first differential amplifier circuit is connected to the output terminal of the second differential amplifier circuit, and the collector forms the output terminal of the first differential amplifier circuit. A sixth transistor in which a DC component of the input signal is applied to a base, and a third current source that supplies a predetermined current to a connection point between the emitters of the fifth and sixth transistors. Have.
[0015]
In the present invention, preferably, the first, second, third and fourth transistors constituting the second and third differential amplifier circuits have substantially the same electrical characteristics.
[0016]
According to the present invention, the DC component of the input signal is extracted by the DC component extraction circuit, and a voltage signal corresponding to the DC component is generated by the first differential amplifier circuit. The voltage signal is fed back to the second differential amplifier circuit. Further, the second differential amplifier circuit generates a signal corresponding to the difference signal between the input signal and its DC component, and the third differential amplifier. The circuit outputs a current signal corresponding to the difference signal. In this way, the DC component of the input signal is canceled, and a current signal that depends only on the amplitude of the input signal can be generated.
[0017]
In addition, since the output signal of the first differential amplifier circuit is fed back to the input side of the second differential amplifier circuit, the linear characteristic of the input impedance of the voltage-current converter circuit is good and signal distortion is minimized. Can be suppressed. In addition, the margin of the dynamic range of the input signal is wide, and low power supply voltage and low power consumption can be realized.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment FIG. 1 is a circuit diagram showing a first embodiment of a voltage-current conversion circuit according to the present invention.
As shown in the figure, the voltage-current conversion circuit of this embodiment includes a low-pass filter composed of a resistor element R1 and a capacitor C1, a differential amplifier circuit AMP1 composed of transistors Q1 and Q2, a current source IS1 and a current mirror circuit ISC1, Differential amplifier circuit AMP2 composed of transistors Q3 and Q4, current source IS2 and current mirror circuit ISC2, differential amplifier circuit AMP3 composed of transistors Q5 and Q6, current source IS3 and current mirror circuit ISC3, and differential amplifier circuit AMP4 It is comprised by.
[0019]
In the voltage-current conversion circuit shown in FIG. 1, the differential amplifier circuits AMP1 to AMP4 are formed inside the IC. Since the voltage-current conversion circuit of the present embodiment is used to amplify an audio signal, the cutoff frequency f _C of the low-pass filter is low, and the capacitor C1 constituting the low-pass filter is formed on the same substrate as other circuit elements. can not be formed, it is provided outside the IC chip via the terminal T _C.
[0020]
Input signal V _in, via a resistor R2, is applied to the base of the transistor Q1, the base and the collector of the transistor Q1 is connected. That is, the transistor Q1 is diode-connected. The emitters of the transistors Q1 and Q2 are connected to each other, and the connection point is connected to the current source IS1. The current mirror circuit ISC1 is connected to the collector side of the transistors Q1 and Q2, and constitutes a dynamic load of these transistors.
[0021]
In the differential amplifier circuit AMP2, the base of the transistor Q3 is connected to the base of the transistor Q2, and the base of the transistor Q4 is connected to the base of the transistor Q1. Further, the emitters of the transistors Q3 and Q4 are connected to each other, and the connection point is connected to the current source IS2. The collectors of the transistors Q3 and Q4 are connected to a current mirror circuit ISC2 that constitutes a dynamic load.
[0022]
In the differential amplifier circuit AMP3, the base of the transistor Q5 is connected to the base of the transistor Q4, and the base of the transistor Q6 is connected to a connection point between the resistor element R1 and the capacitor C1 constituting the low-pass filter, that is, the terminal T _C. Has been. The emitters of the transistors Q5 and Q6 are connected to each other, and the connection point is connected to the current source IS3. The collectors of the transistors Q5 and Q6 are connected to a current mirror circuit ISC3 that constitutes a dynamic load.
[0023]
The inverting input terminal (−) of the differential amplifier circuit AMP4 is connected to the collector of the transistor Q4 of the differential amplifier circuit AMP2, the input terminal (+) is connected to one terminal of the resistor element R4, and the other terminal of the resistor element R4. The terminal is connected to the voltage source VS1.
[0024]
In the circuit shown in FIG. 1, the resistance element R2 is an input resistance element, and the resistance element R3 is an output resistance element. The voltage source VS1 is provided to provide an offset of the output voltage _Vout .
[0025]
Figure 2 is a waveform diagram showing a waveform of an input signal V _in and the output signal V _out of the circuit shown in FIG. As shown in FIG. 2 (a), the input signal V _in includes the DC component V _DC, between the DC component V _DC to the desired bias voltage V1, there is an offset. Voltage of this embodiment - by a current converter circuit, the DC component V _DC of the input signal V _in is removed. As shown in FIG. 5B, a desired offset voltage V1 is set to the output signal _Vout by the voltage source VS1. As a result, the output signal _Vout is in the center bias state.
[0026]
Hereinafter, the operation of the voltage-current conversion circuit of this embodiment will be described with reference to FIG.
When the level of the input signal V _in is changed by [Delta] V _in, and the current generated in the resistor elements R2 and i _in, the collector current i _c1 of transistor Q1 becomes (i _in + i _cs1). That is, (i _c2 = i _cs1 = i _c1 −i _in ). Here, i _cs1 is a current value of the current mirror circuit ISC1. Further, when the current value of the current source IS1 is i ₁ , the following equation is obtained.
[0027]
[Expression 2]
i ₁ = i _c1 + i _c2 = 2i _c1 −i _in
i _c1 = (i ₁ + i _in ) / 2 (2)
[0028]
The collector current i _c2 of transistor Q2 is determined by the following equation.
[0029]
[Equation 3]
i _c2 = i ₁ −i _c1 = (i ₁ −i _in ) / 2 (3)
[0030]
Here, if the saturation voltages of the transistors Q1 and Q2 are i _s1 and i _s2 , the base-emitter voltages V _be1 and V _be2 of the transistors Q1 and Q2 are V _t ln (i _c1 / i _s1 ) and V _{t, respectively.} Since it is expressed by ln (i _c2 / i _s2 ), the following equation is obtained.
[0031]
[Expression 4]

(4)
[0032]
When the current value of the current mirror circuit ISC2 is i _cs2 and the output current is i _out , the collector current i _c4 of the transistor Q4 is (i _out + i _cs2 ). That is, (i _c3 = i _cs2 = i _c4 −i _out ). If the current value of the current source IS2 and i _2, the following equation is obtained.
[0033]
[Equation 5]
i ₂ = i _c3 + i _c4 = 2 i _c4 −i _out
i _c4 = (i ₂ + i _out ) / 2 (5)
[0034]
Further, the collector current i _c3 of the transistor Q3 is determined by the following equation.
[0035]
[Formula 6]
i _c3 = i ₂ −i _c4 = (i ₂ −i _out ) / 2 (6)
[0036]
Here, _assuming that the saturation voltages of the transistors Q3 and Q4 are i _s3 and i _s4 , the base-emitter voltages V _be3 and V _be4 of the transistors Q3 and Q4 are V _t ln ( _{ic 3} / i _s3 ) and V _{t, respectively.} Since it is expressed by ln (i _c4 / i _s4 ), the following equation is obtained.
[0037]
[Expression 7]

... (7)
[0038]
As illustrated, when the base voltage of the transistor Q1 is V1, and the base voltage of the transistor Q2 or Q3 is V2, the following equation is obtained.
[0039]
[Equation 8]
V1-V _be1 = V2-V _be2
V1−V2 = V _be1 −V _be2 (8)
[0040]
[Equation 9]
V2-V _be3 = V1-V _be4
V1−V2 = V _be4 −V _be3 (9)
[0041]
Here, assuming that the transistors Q1, Q2, Q3, and Q4 have the same electrical characteristics, the saturation currents i _s1 , i _s2 , i _s3 , and i _s4 of these transistors have the same value. .
[0042]
From the equations (8) and (9), the following equation is obtained.
[0043]
[Expression 10]
V _be1 −V _be2 = V _be4 −V _be3 (10)
[0044]
Substituting equations (4) and (7) into equation (10) yields:
[0045]
[Expression 11]
(I ₁ + i _in ) / (i ₁ −i _in ) =
(I ₂ + i _out ) / (i ₂ −i _out )
i _out = i _in · i ₂ / i ₁ (11)
[0046]
Here, if (i ₁ = i ₂ ), that is, if the current values of the current sources IS1 and IS2 are equal, (i _out = i _in ).
In the differential amplifier circuit AMP4, when the resistance value of the output resistance element R3 is r3, (V _out = i _out · r3).
[0047]
Further, when the resistance value of the output resistor element R3 and the input resistor element R2 are the same, depending on the amount of change [Delta] V _in the input signal V _in, the amount of change [Delta] V _out generated in the output signal V _out is equal to [Delta] V _in . That is, (ΔV _out = ΔV _in ).
[0048]
As described above, when the input signal Vin is input as a signal having the DC component V _DC as shown _in FIG. 2A, the DC component V is received by the low-pass filter composed of the resistor element R1 and the capacitor C1. _DC is extracted. The extracted DC component V _DC is input to the differential amplifier circuit AMP3, and a voltage V2 corresponding to the DC component V _DC is applied to the bases of the transistors Q2 and Q3 of the differential amplifier circuits AMP1 and AMP2, respectively. That is, the voltage V2 generated according to the direct current component V _DC is fed back to the negative input side of the differential amplifier circuit AMP1, whereby the bases of the transistors Q5 and Q6 of the differential amplifier circuit AMP3 are imaginarily short-circuited, and the voltage V1 And the DC component V _DC are equal. This does not include the direct-current component V _DC of the input signal V _in to an output current i _out, only pure AC component is transferred.
[0049]
Further, by feeding back the DC component V _DC to the negative side of the differential amplifier circuit AMP1 differential amplifier circuit AMP3, by suppressing it, in the differential amplifier circuit AMP1, the emitter resistor r _e of the transistor Q1 serving as a diode-connected Does not appear in the input impedance, and the input impedance viewed from the input terminal is purely only the input resistance R2, so that the linear characteristic of the circuit is good and signal distortion can be reduced.
[0050]
As described above, according to this embodiment, the low-pass filter constituted by the resistor element R1 and the capacitor C1, to extract the DC component V _DC of the input signal V _in, input to the differential amplifier circuit AMP3, accordingly The generated voltage V2 is generated by the differential amplifier circuit AMP3 and fed back to the negative input side of the differential amplifier circuit AMP1, so that the base of the transistor Q1 of the differential amplifier circuit AMP1 is held at the same potential as the DC component _VDC . Moreover, the base of the transistor Q1, so applies an input signal V _in via an input resistor element R2, the difference signal of the input signal V _in and its DC component V _DC is generated by the differential amplifier circuit AMP2, the Since the output current i _out corresponding to the difference signal is generated, the current i _out does not include the DC component V _DC and depends only on the amplitude of the input signal.
As a result, the linear characteristics of the circuit can be improved, the distortion of the signal can be reduced, and the resistance element of the low-pass filter for extracting the DC component can be increased, so that the capacitor connected to the outside of the IC chip can be increased. The capacity can be reduced and the cost of external parts can be reduced. In addition, it is possible to realize a low power supply voltage operation without using the current source repeatedly to cancel the offset.
[0051]
Second Embodiment FIG. 3 is a circuit diagram showing a second embodiment of the voltage-current conversion circuit according to the present invention.
As shown in the figure, the voltage-current conversion circuit of this embodiment is different from the first embodiment of the present invention shown in FIG. 1 in the configuration of the differential amplifier circuit AMP1, and all other parts are the same. is there. In FIG. 3, the same circuit elements as those in FIG. 1 and circuit portions having the same configuration are denoted by the same reference numerals.
[0052]
In the present embodiment, in the differential amplifier circuit AMP1, a variable current source ISV1 is connected to a connection point between the emitters of the transistors Q1 and Q2. The level of the output signal _Vout can be adjusted by controlling the supply current of the variable current source ISV1.
[0053]
The amount of change ΔV _out of the output signal V _out can be adjusted by controlling the current value i ₁ or i ₂ of the current source IS1 or IS2 by the above-described equation (11). Therefore, as shown in FIG. 3, the change amount [Delta] V _in the input signal V _in is constant, that is, when i _in is constant, if the current set large for the variable current source ISV1, the output signal V _out If the amount of change ΔV _out decreases, conversely, if the current of the conversion current source ISV1 is set small, the amount of change ΔV _out of the output signal increases.
[0054]
Thus, by controlling the current value supplied to the differential amplifier circuit AMP1, the level of the output signal can be controlled, and for example, an electronic volume for adjusting the volume can be realized.
[0055]
As described above, according to this embodiment, the drive current is supplied to the differential amplifier circuit AMP1 by the variable current source ISV1, and the current of the ISV1 is controlled by the variable current source, thereby controlling the amplitude of the output signal. Electronic volume can be realized.
The amplitude control of the output signal can be realized not only by controlling the drive current source of the differential amplifier circuit AMP1, but also by controlling the current of the drive current source of the differential amplifier circuit AMP2.
[0056]
Third Embodiment FIG. 4 is a circuit diagram showing a third embodiment of the voltage-current conversion circuit according to the present invention.
As illustrated, in the present embodiment, a transistor Q7 is newly provided in the differential amplifier circuit AMP2 as compared with the second embodiment described above.
The collector of the transistor Q7 is connected to the power supply voltage V _CC , the base is connected to the variable voltage source VS2, and the emitter is connected to the connection point between the emitters of the transistors Q3 and Q4.
[0057]
In the voltage-current conversion circuit having the configuration shown in FIG. 4, the amplitude of the output signal _Vout can be controlled by controlling the current of the variable current source ISV1 of the differential amplifier circuit AMP1. That is, the volume of the output signal can be adjusted. Further, by controlling the voltage value v3 of the variable voltage source VS2, a so-called mute function for maintaining the amplitude of the output signal _Vout at 0 can be realized.
[0058]
In the differential amplifier circuit AMP2, the base voltage of the transistor Q3 is V2. As described above, the voltage V2 becomes equal to the DC component V _DC of the input signal V _in. Adjust the voltage value V3 of the variable voltage source VS2, when set higher than V2, the transistor Q7 is turned on, the emitter of the transistor Q7, the same current i ₇ and the current value i ₂ of the current source IS2 flows. For this reason, the output current i _out becomes zero. Amplitude of the output signal V _out of _the differential amplifier AMP4 accordingly also held to zero.
[0059]
As described above, according to the present embodiment, the transistor Q7 is provided in the differential amplifier circuit AMP2, the emitter of the transistor Q7 is connected to the emitters of the transistors Q3 and Q4, and applied to the base of the transistor Q7. By controlling the level of the voltage V3 and controlling the on / off state of the transistor Q7, a mute function can be realized.
The voltage value from the DC component V _DC of the input signal V _in in place of the variable voltage source VS2 is provided a fixed voltage source for supplying a high voltage V3, between the base and the fixed voltage source of the transistor Q7, the switch Needless to say, the same mute function can be realized by controlling the on / off state of the switch.
[0060]
Fourth Embodiment FIG. 5 is a circuit diagram showing a fourth embodiment of the voltage-current conversion circuit according to the present invention.
As shown in the figure, the voltage-current conversion circuit of the present embodiment is newly provided with a differential amplifier circuit AMP5 and a differential amplifier circuit AMP6 as compared with the first embodiment shown in FIG.
[0061]
The differential amplifier circuit AMP5 includes transistors Q8 and Q9, a current source IS4, and a current mirror circuit ISC4. As illustrated, the differential amplifier circuit AMP5 is provided in parallel with the differential amplifier circuit AMP2. That is, the base of the transistor Q8 is connected to the base of the transistor Q3, and the base of the transistor Q9 is connected to the base of the transistor Q4. The emitters of the transistors Q8 and Q9 are connected to each other, and the connection point is connected to the current source IS4. Further, the collectors of the transistors Q8 and Q9 are connected to a current mirror circuit ISC4 constituting a dynamic load.
[0062]
The inverting input terminal (−) of the differential amplifier circuit AMP6 is connected to the collector of the transistor Q9 of the differential amplifier circuit AMP5, the input terminal (+) is connected to one terminal of the resistor element R6, and the other terminal of the resistor element R6. The terminal is connected to the voltage source VS3.
[0063]
Here, for example, when the transistors Q8 and Q9 constituting the differential amplifier circuit AMP5 have the same electrical characteristics as the transistors Q1 to Q4 constituting the other differential amplifier circuits AMP1 and AMP2, the differential amplifier circuit AMP5. Thus, an output current i _out2 is obtained. Note that (i _out2 = i _out1 ).
[0064]
Thus, for example, by setting the voltage value of the voltage source VS3 to be different from the voltage sources VS1, can acquire an output signal V _out2 having an output signal V _out1 and different offset. Thus, from one of the input signal V _in, it is possible to obtain a plurality of output voltages. If necessary, the offsets of the plurality of output signals can be set to different values.
[0065]
As described above, according to this embodiment, provided with a differential amplifier circuit AMP5 in parallel with the differential amplifier circuit AMP2, further by providing a differential amplifier circuit AMP6 at its output, the input signal V _in Accordingly, a plurality of output currents can be generated, and a plurality of output voltages having different offsets can be generated according to these output currents.
[0066]
【The invention's effect】
As described above, according to the voltage-current conversion circuit of the present invention, the DC component of the input signal is extracted and supplied to the differential amplifier circuit, thereby generating a voltage corresponding to the DC component, By feeding back to the inverting input side of the differential amplifier circuit, the DC component of the input signal can be canceled. In addition, since the resistance element of the low-pass filter that extracts the DC component of the input signal can be set large, there is an advantage that the capacitance of the capacitor can be reduced and the cost of external parts can be reduced.
Furthermore, by feeding back the voltage to the inverting input side of the differential amplifier circuit that cancels the DC component according to the DC component of the input signal, the linear characteristic of the input impedance of the circuit is good, and signal distortion can be reduced. Furthermore, according to the present invention, a voltage-current conversion circuit with low voltage and low power consumption can be realized.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a first embodiment of a voltage-current conversion circuit according to the present invention.
FIG. 2 is a waveform diagram showing waveforms of input / output signals according to the first embodiment.
FIG. 3 is a circuit diagram showing a second embodiment of a voltage-current conversion circuit according to the present invention.
FIG. 4 is a circuit diagram showing a third embodiment of a voltage-current conversion circuit according to the present invention.
FIG. 5 is a circuit diagram showing a fourth embodiment of a voltage-current conversion circuit according to the present invention.
FIG. 6 is a circuit diagram showing an example of a conventional voltage-current conversion circuit.
[Explanation of symbols]
AMP1, AMP2, AMP3, AMP4, AMP5, AMP6 ... differential amplifier circuit, IS1, IS2, IS3, IS4 ... current source, VS1, VS2, VS3 ... voltage source, R1, R2, R3, R4, R5, R6 ... resistor element, C1 ... capacitor, ISC1, ISC2, ISC3, ISC4 ... current mirror circuit, T _C ... capacitor connection terminal, V _CC ... power supply voltage, GND ... ground potential.

Claims (17)

A voltage-current conversion circuit that outputs a current signal corresponding to the amplitude of an input signal whose level fluctuates up and down around a predetermined DC component,
A DC component extraction circuit for extracting a DC component of the input signal;
A first differential amplifier circuit that inputs the extracted DC component to a non-inverting input terminal and outputs a voltage signal from an output terminal according to the DC component;
An inverting input terminal is connected to the input terminal of the input signal via a resistance element, an output signal of the first differential amplifier circuit is applied to the non-inverting input terminal, and an output terminal is connected to the inverting input terminal A second differential amplifier circuit,
The output signal of the first differential amplifier circuit is input to one input terminal, and the output signal of the second differential amplifier circuit is input to the other input terminal together with the inverting input terminal of the first differential amplifier circuit. And a third differential amplifier circuit for inputting and outputting a current signal corresponding to the difference between the input signal and its DC component. 2. The voltage-current conversion circuit according to claim 1, wherein the DC component extraction circuit comprises a low-pass filter having a cutoff frequency set in accordance with the frequency of the input signal. The low-pass filter includes a resistance element and a capacitor connected in series between an input terminal of the input signal and a common potential, and a DC component of the input signal is output from a connection point between the resistance element and the capacitor. Item 3. The voltage-current conversion circuit according to Item 2. 4. The voltage-current conversion circuit according to claim 3, wherein the capacitor is connected to the outside of the IC chip. The second differential amplifier circuit includes a first transistor whose base is connected to the input terminal of the input signal via the resistor element, and whose collector forms the output terminal of the second differential amplifier circuit. ,
A second transistor having a base connected to the output terminal of the first differential amplifier circuit;
2. The voltage-current conversion circuit according to claim 1, further comprising a first current source for supplying a predetermined current to a connection point between the emitters of the first and second transistors. 6. The voltage-current conversion circuit according to claim 5, wherein a base and a collector of the first transistor are connected. 6. The voltage-current conversion circuit according to claim 5, wherein the current of the first current source is variable. A third transistor having a base connected to an output terminal of the first differential amplifier;
A fourth transistor, the base of which is connected to the output terminal of the second differential amplifier circuit, and the current signal is supplied to the outside from the collector;
2. The voltage-current conversion circuit according to claim 1, further comprising a second current source for supplying a predetermined current to a connection point between the emitters of the third and fourth transistors. 9. The voltage-current conversion circuit according to claim 8, wherein the current of the second current source is variable. The first differential amplifier circuit has a base connected to the output terminal of the second differential amplifier circuit, and a collector forming a fifth transistor forming the output terminal of the first differential amplifier circuit;
A sixth transistor having a DC component of the input signal applied to the base;
6. The voltage-current conversion circuit according to claim 5, further comprising a third current source for supplying a predetermined current to a connection point between the emitters of the fifth and sixth transistors. The second differential amplifier circuit includes a first transistor whose base is connected to the input terminal of the input signal via the resistor element, and whose collector forms the output terminal of the second differential amplifier circuit. ,
A second transistor having a base connected to the output terminal of the first differential amplifier circuit;
A first current source for supplying a predetermined current to a connection point between the emitters of the first and second transistors;
A third transistor having a base connected to an output terminal of the first differential amplifier;
A fourth transistor, the base of which is connected to the output terminal of the second differential amplifier circuit, and the current signal is supplied to the outside from the collector;
2. The voltage-current conversion circuit according to claim 1, further comprising a second current source for supplying a predetermined current to a connection point between the emitters of the third and fourth transistors. 12. The voltage-current conversion circuit according to claim 11, wherein the first, second, third, and fourth transistors constituting the second and third differential amplifier circuits have substantially the same electrical characteristics. A current that cancels the supply current of the second current source is supplied to a connection point between the emitters of the third and fourth transistors constituting the third differential amplifier circuit, and the current signal is output. The voltage-current conversion circuit according to claim 11, further comprising a current source that suppresses current. 12. The voltage-current conversion circuit according to claim 11, further comprising an output circuit for generating a voltage signal having an amplitude corresponding to a current signal of the third differential amplifier circuit and having a predetermined DC component. A seventh transistor whose base is connected to the base of the third transistor;
An eighth transistor having a base connected to the base of the fourth transistor and a predetermined current signal supplied from the collector to the outside;
12. The voltage-current circuit according to claim 11, further comprising a fourth differential amplifier circuit configured by a fourth current source that supplies a predetermined current to a connection point between the emitters of the seventh and eighth transistors. Conversion circuit. 16. The voltage-current conversion circuit according to claim 15, wherein the seventh and eighth transistors have substantially the same electrical characteristics as the first, second, third, and fourth transistors. 16. The voltage-current conversion according to claim 15, further comprising a second output circuit that generates a second voltage signal having an amplitude corresponding to the current signal of the fourth differential amplifier circuit and having a predetermined DC component. circuit.

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