JPH0511526U - Compound amplifier circuit - Google Patents

Abstract

(57) [Summary] [Purpose] When applying DC bias to arbitrary waveform signals,
Good (ie constant) from DC to high frequency bands
A composite amplifier circuit having a gain characteristic is provided. [Structure] The feedback loops of the first and second operational amplifiers 1 and 2 are resistors R _{1 to} R ₄ which constitute both sets of a two-resistor series connection circuit.
(R ₂ / R ₁ = R ₄ / R ₃ ). For example, if the value of R ₀ is set sufficiently larger than R ₃ and R ₄ , a DC voltage of − (R ₂ / R ₁ ) times the DC bias V _b appears as a DC component.
Of the frequency components forming the arbitrary waveform signal input from the terminal a, the second operational amplifier mainly performs the amplifying operation for the high frequency component and the first and second operational amplifiers perform the amplifying operation for the low frequency component. Handle. At the output terminal c of the composite amplifier circuit, a voltage of 1+ (R ₂ / R ₁ ) times the input signal V _a appears as an amplification component for the arbitrary waveform signal. Then, the addition value of V _{a at a} frequency of 100 MHz or more and the DC bias V _b from the terminal b, {1+ (R ₂ /
R ₁ )} V _a − (R ₂ / R ₁ ) V _b is output with a precision of 16 bits or more.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a composite amplifier circuit used in a waveform generation device in an LSI tester or the like, for example. The present invention relates to the above-mentioned amplifier circuit that can be generated with accuracy.

[0002]

[Technical background]

 For example, in an LSI test system, a signal obtained by adding a DC bias to an arbitrary waveform signal such as a rectangular wave or a sawtooth wave may be used as a test signal. Conventionally, a non-inverting amplification circuit as shown in FIG. 4 has been known as a circuit for generating such a signal. In the circuit of the figure, the high-speed arbitrary waveform signal V_aIs input to the terminal b and the DC bias signal V_bIs entered. V_aIs input to the non-inverting input terminal (+) of the operational amplifier 11 for wide band, and V_bIs a resistor R at the inverting input terminal (-) of the amplifier 11.₁₁ Input via. Further, a feedback resistor R is provided between the output terminal and the inverting input terminal of the operational amplifier 11.₁₂Are connected. In addition, in FIG. 4, a resistor R is provided on the input side and the output side._inAnd R_outAre connected respectively. In the circuit having the above configuration, the output voltage V_cTo V_aAnd V_bIs expressed as V_c= {1+ (R₁₂/ R₁₁)} V_a-(R₁₂/ R₁₁) V_b Becomes However, it is difficult to obtain a high-precision DC characteristic in a wide frequency band in a wide-band type such as the operational amplifier 11 shown in FIG. 4, and the accuracy of linearity is 10 bits (accuracy: 1/2^Ten) There is a disadvantage that it is nothing more than. A composite amplifier circuit as shown in FIG. 5 is also known (see Japanese Utility Model Publication No. 3-23690). In this amplifier circuit, the output terminal of the low drift operational amplifier 21 for low frequencies and the input terminal of the wide band operational amplifier 22 are connected to a filter 23 (C_{twenty one}, C_{twenty two}And R _{twenty two} The output terminal c and the inverting input terminal of each operational amplifier 21, 22 are connected to the feedback resistor R._{twenty five}, R₂₆Are connected. Also, in the figure, the resistor R for bias is_{twenty three}, R_{twenty four}Is provided, and a resistor R is provided between the input terminal a and the non-inverting input terminal of the operational amplifier 21._{twenty one}Are connected. In this circuit, the arbitrary waveform signal V_aThe low frequency component of the frequency component is amplified by the operational amplifier 21, and the high frequency component is amplified by the amplifier 22 to avoid the drift. However, this circuit has a disadvantage that the gain characteristic is rapidly deteriorated in the vicinity of the frequency at the boundary between the operation region of one operational amplifier and the operation region of the other operational amplifier. Also, in order to reduce this inconvenience, a circuit in which a buffer circuit is provided between both operational amplifiers 21 and 22 is also described in the above publication, but in this case there is a problem that the circuit configuration becomes complicated.

[0003]

[The purpose of the device]

 The present invention has been proposed to solve the above problems, and when a DC bias is applied to an arbitrary waveform signal, a good (that is, constant) gain is obtained from DC to a high frequency band. An object is to provide a composite amplifier circuit having characteristics.

[0004]

[Outline of the device]

The circuit of the present invention comprises a two-stage amplifier circuit of a first operational amplifier having a high precision DC characteristic and a second operational amplifier having a wide band frequency characteristic. The arbitrary waveform signal input terminal is connected to each non-inverting input terminal of both operational amplifiers, and the output terminal of the first operational amplifier is connected to the inverting input terminal of the second operational amplifier via the connection resistor R _0. It Further, between the DC bias input terminal and the output terminal of the second operational amplifier, two sets of two resistance series connection circuits (both sets are connected in series with R ₁ and R ₂ and with R ₃ and R ₄ the series connection circuit has (see FIG. 1)) is connected in parallel, the ratio of the resistance value in each set are chosen to be equal in both sets _{(i.e., R 2 / R 1 = R} 4 / R ₃ ). The connection point of the two resistors in each set is connected to each inverting input terminal of the first and second operational amplifiers. Here, it is assumed that the connection point of R ₁ and R ₂ is connected to the reverse input terminal of the first operational amplifier, and the connection point of R ₃ and R ₄ is connected to the inverting input terminal of the second operational amplifier. ..

In the present invention, the feedback loops of the first and second operational amplifiers are composed of resistors that form both sets of the above-mentioned two-resistor series connection circuit, and The ratios are chosen to be equal. In addition, R₀An appropriate value as (ie, R of the first operational amplifier)₀By setting the output resistance including the value to an appropriate value), the amplification factor of the composite amplifier circuit of the present invention can be set to a desired value regardless of the frequency of the arbitrary waveform input to the first operational amplifier ( Equation 10). By the way, since the characteristics of the operational amplifier vary, the amplification factor of the composite amplifier circuit itself may not be constant. In such a case, the connecting resistor R ₀ The value of R₃, R_FourIt can be made sufficiently large to cancel the variation in the characteristics of the operational amplifier. Assuming that the DC gain of the operational amplifier is ideal (that is, ∞), the output terminal of the circuit of the present invention has a DC bias V as a DC component._b-(R₂/ R₁) Double DC voltage appears. Here, since the first operational amplifier has a high precision DC characteristic, the offset amount of the operational amplifier is ignored. Of the frequency components forming the arbitrary waveform signal input from the external signal input terminal, the second operational amplifier is mainly used for high frequency components and the first and second operational amplifiers are used for low frequency components (including direct current). The operational amplifiers are respectively responsible for the amplification operation. At this time, at the output terminal of the composite amplification circuit of the present invention, as an amplification component of the arbitrary waveform signal (a portion of the output signal excluding the DC bias component), For example, R₀Is sufficiently large, the input signal V_aOf {1+ (R_Four/ R₃)} (R₂/ R₁= R_Four / R₃So, {1+ (R₂/ R₁)}) Double voltage appears. In this way, if the first operational amplifier has a high precision DC characteristic, even if the operational amplifier DC precision having the second wide band characteristic is low, the composite amplifier circuit of the present invention provides a high precision ( An output of 16 bits or more) can be obtained. For example R ₀ When the value of is sufficiently large, the arbitrary waveform signal V with a frequency of 100 MHz or higher input from the external signal input terminal_aAnd DC bias V_bAnd the addition value, {1+ (R₂/ R₁)} V_a-(R₂/ R₁) V_b Is output with a precision of 16 bits or more.

[0006]

【Example】

 FIG. 1 is a circuit diagram showing an embodiment of the present invention. This circuit is equipped with an operational amplifier 1 (amplification factor: L (ω)) having high precision DC characteristics and a high-speed operational amplifier 2 (amplification factor: H (ω)) having wide band frequency characteristics. L (ω) and H (ω) are functions of the angular frequency ω of the input signal. The input terminal a to which the arbitrary waveform signal is input is connected to the non-inverting input terminal (+) of the operational amplifier 1 and the non-inverting input terminal (+) of the operational amplifier 2 through the resistor R '. In addition, R is connected between the DC bias input terminal b and the output terminal of the second operational amplifier 2.₁ , R₂2-resistor series connection circuit and R₃, R_FourThe two-resistor series connection circuit consisting of the group is connected in parallel, and the resistance value ratio in each group is selected to be the same in both groups.₁~ R_FourR between₂/ R₁= R_Four/ R₃The following relationship is established. And 2 resistors R in each set₁, R₂And R₃, R_FourIs connected to each inverting input terminal (-) of the first and second operational amplifiers 1 and 2. The output terminal of the operational amplifier 1 has a connection resistor R₀1 is connected to the inverting input terminal (-) of the operational amplifier 2 via the input resistor R between the arbitrary waveform signal input terminal a and the ground in FIG._inHowever, there is a resistor R between the output terminal c and the output terminal of the operational amplifier 2. _out Are connected respectively.

The operation of the above circuit will be described in detail below with reference to FIGS. 2 and 3. Note that, for convenience, R ₀ includes the output resistance of the operational amplifier 1 itself. FIG. 2 is a circuit diagram when the external input terminal a is grounded (V _a = 0), and the offset voltages of the operational amplifiers 1 and 2 are represented by e ₀₁ and e ₀₂ . first operational amplifier 1 of the output voltage e _1, the input voltage of the e ₂ to the inverting input terminal of the operational amplifier 2 (i.e., R _0, R _3, connecting point voltage of R ₄₎ When to, times in FIG. 2 The path equation is expressed as follows.

[Equation 1]

[Equation 2]

[Equation 3]

By erasing and arranging e ₁ and e ₂ from Equations ₁ , ₂ , and 3,

[Equation 4] Becomes Here, with respect to the DC bias V _b , since the amplification factors of the operational amplifiers 1 and 2 can be infinite, if L (ω), H (ω) → ∞ in Equation 4,

[Equation 5] Becomes The operational amplifier 1 has a high-precision DC characteristic, and the offset can be 0 (e ₀₁ ≈0).

[Equation 6] Can be regarded as

FIG. 3 is a circuit diagram when the offset input b is set to the ground potential (V _b = 0), and the circuit equation is expressed as follows.

[Equation 7]

[Equation 8]

[Equation 9]

As in the case of FIG. 3, when erasing and arranging e ₁ and e ₂ from Equations 7, 8, and 9,

[Equation 10] Becomes Here, since L (ω) and H (ω) are considered to be sufficiently large in the low frequency band, if L (ω), H (ω) → ∞ in Formula 10, V _c → {1+ (R ₂ / R ₁ )} V _a .

Further, in a high frequency band, the amplification factor of L (ω) can approach 0. Assuming that L (ω) → 0 and H (ω) → ∞ in Expression 9, V _c → R ₄ {(1 / R ₀ ) + (1 / R ₃ ) + (1 / R ₄ )} V _a. .. By the way, as described above, R ₀ includes the output resistance of the operational amplifier 1. Therefore, the composite amplifier itself may also vary due to the variation in the output resistance of each operational amplifier 1. Therefore, in such a case, if the actual resistance value connected to the output terminal of the operational amplifier 1 is selected so that R ₀ >> R ₃ and R ₄ , V _c ≈ {1+ (R ₄ / R ₃ )} V _a, and the variation in the output resistance of the operational amplifier 1 itself can be canceled. Here, R _{1 to} R ₄ are selected such that R ₃ / R ₄ = R ₁ / R ₂ , so the above equation is V _c ≈ {1+ (R ₂ / R ₁ )} V the _a.

In this case, the amplification factor V _c / V _a of the composite amplifier converges to the same amplification factor 1+ (R ₂ / R ₁ ) in both the low frequency region and the high frequency region. .. The output voltage V _c in FIG. 1 is expressed as V _c ≈ {1+ (R ₂ / R ₁ )} V from the equation 6 expressing the output voltage for the DC bias component and the above equation expressing the output voltage for the arbitrary waveform signal. _a - it is expressed as _{(R 2 / R 1) V} b. The description is omitted for the case where L (ω) is a finite value other than 0. However, in this case as well, if the value of R ₀ is appropriately selected, the relationship of the above equation is established, and the composite amplification of FIG. The characteristics of the circuit can be kept constant.

[0013]

[Effect of the device]

 As described above, in the composite operational amplifier circuit of the present invention, it is possible to obtain an output having a high precision DC characteristic in which a DC bias is applied to a high-speed arbitrary waveform signal from DC to a high frequency band of 100 MHz or more. .. Especially in terms of linearity, an accuracy of 16 bits or more can be realized. Further, it is possible to provide an operational amplifier circuit that can achieve the above effect with a simple circuit without separately providing a buffer circuit.

[Brief description of drawings]

FIG. 1 is a diagram showing an operational amplifier circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a case where the input terminal of the arbitrary waveform signal in FIG. 1 is grounded.

FIG. 3 is a circuit diagram showing a case where an input terminal for DC bias in FIG. 1 is grounded.

FIG. 4 is an adder circuit diagram showing the operation of a conventional operational amplifier.

FIG. 5 is a circuit diagram showing a conventional wideband composite operational amplifier circuit.

[Explanation of symbols]

1: First operational amplifier having high precision DC characteristics 2: Second operational amplifier having wide band frequency characteristics a: Arbitrary waveform signal input terminal b: DC bias input terminal c: Output terminal of composite operational amplifier circuit R ₀ : connected resistors R ₁ to R _4: 2 resistor V _a constituting the resistor series circuit: arbitrary waveform signal V _b: DC bias V _c: output of the combined operational amplifier circuit

Claims (1)

Claims for utility model registration 1. A composite amplifier circuit comprising an operational amplifier circuit in which a first operational amplifier having high-precision DC characteristics and a second operational amplifier having wideband frequency characteristics are connected. The arbitrary waveform signal input terminal is connected to each non-inverting input terminal of the first and second operational amplifiers, and the output terminal of the first operational amplifier is connected to the inverting input of the second operational amplifier via the connection resistor. A parallel circuit consisting of two sets of two-resistor series-connected circuits connected to the terminals and between the DC bias input terminal and the output terminal of the second operational amplifier. A composite amplifier circuit characterized in that circuits selected so as to be equal in both groups are connected, and a connection point of two resistors in each group is connected to each inverting input terminal of the first and second operational amplifiers. ..