JP2007006402A - Feedback signal processing circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a feedback signal processing circuit having a transfer function with a modified loop gain so that the transmission gain in a passing frequency region becomes negative feedback no greater than a forward gain, so as to obtain a low noise characteristic. <P>SOLUTION: The feedback signal processing circuit includes a forward circuit for applying a predetermined transfer characteristic to an input signal, so as to output with a predetermined gain, and a feedback circuit for negative feedbacking a portion of the output of the forward circuit to the input signal. The forward circuit is a current-controlled voltage output circuit, including a base-grounded transistor to which the input signal is input, a circuit having a transfer impedance characteristic, and an emitter-follower transistor for outputting voltage. The above current-controlled voltage output circuit may also be configured by use of an operational amplifier. The transfer impedance characteristic is achieved by a variety of types of high-pass, low-pass and band pass filters. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a feedback signal processing circuit, and more particularly, a high-pass filter or a low-pass filter is obtained by giving a frequency-dependent transfer characteristic to a forward circuit and attenuating gain by negatively feeding back in a pass frequency range. The present invention relates to a feedback signal processing circuit that obtains transfer impedance characteristics.

  Recent advances in electronics technology are remarkable, and it has become common knowledge that electronic circuits are integrated and signal processing is digitized. Among them, downsizing and integration of continuous-time filters essential for analog signal processing have progressed in the form of active RC filters. With the recent digitalization, the use of the high frequency region is progressing, but it is difficult to cope with the high frequency region, and it has been developed to increase the frequency and integration of active RC filters for signal processing in the high frequency region. It has been done. In addition, continuous-time filters are superior in signal processing where noise is a problem even in intermediate and low frequency bands, and active RC filters and integration have been developed for this purpose.

  The active secondary circuit which is the basis of such an active RC filter includes a salen key circuit using a positive phase amplifier, a single amplifier type circuit, a circuit using a gyrator, and the like. However, the Salen-Key circuit approaches a positive feedback at the pole frequency (center frequency), and the Q element sensitivity is extremely high. In a single-amplifier type circuit using a multiple feedback system, a stable high Q can be realized, but a forward gain including an open-circuit gain of an operational amplifier is obtained at a pole frequency. In the case of a gyrator using a transistor, it is easy to obtain a stable high Q in a high frequency range, but it is difficult to reduce noise because the loop gain approaches positive feedback at a pole frequency. .

  In this way, when a filter circuit based on an active secondary circuit such as a Salen-Key circuit using a positive phase amplifier, a circuit using a single amplifier, or a circuit using a gyrator is configured, in either case Although it is convenient for obtaining a high Q, it is difficult to keep the noise low because the negative feedback state does not occur at the pole frequency of the circuit, and this noise problem has not been solved.

  Obtaining a stable high Q in the high frequency range and achieving low noise have not been solved. Therefore, at present, an active RC filter in the high frequency range has not been put into practical use. Actually, a passive coil (chip inductor) must be used to form a filter circuit in a high frequency region, and this passive coil is externally attached. As a result, miniaturization and monolithic IC of various filter circuits, particularly in the high frequency range, has become a problem.

  Therefore, various filter circuits including a wide range of inductances must be easily integrated with other circuits, and the circuit configuration must be downsized. To date, in order to achieve low noise characteristics, A feedback type signal processing circuit having a transfer function for changing the loop gain has been developed so that the transmission gain at the center is a negative feedback less than the forward gain (see, for example, Patent Document 1, Non-Patent Documents 1 and 2). ).

  In the feedback type signal processing circuit developed above, the basic principle that the transmission gain in the entire frequency range is negative feedback with a forward gain or less will be described with reference to FIG. In the signal processing circuit, a feedback type is adopted as an active RC filter circuit. A block diagram of the signal processing circuit in the feedback format is shown in FIG.

In FIG. 17, I _i represents an input current, I _o represents an output current, and the transfer function of the forward circuit unit is T ₁ (s) and the transfer function of the feedback circuit unit is T ₂ (s ). Therefore, the input / output transfer function T (s) in the feedback circuit shown in FIG. 17 is expressed as follows.
T (s) = I _o / I _i
= T ₁ (s) / {1-T ₁ (s) · T ₂ (s)} (1)

Here, in order to make the characteristics of the feedback signal processing circuit shown in FIG. 17 negative feedback whose transmission gain is equal to or less than the forward gain in the entire frequency range, the input / output transfer function T in Expression (1) is used. Based on (s),
| T (s) | ≦ | T ₁ (s) | (2)
It is necessary to satisfy the conditions. Therefore, the target filter characteristics are realized by selecting transfer functions T ₁ (s) and T ₂ (s) that satisfy the condition expressed by the equation (2).

However, in the circuit configuration of FIG. 17, it is difficult to satisfy the condition of the expression (2) in the entire frequency range including the pole frequency, and therefore the constant a where a> 1 is set to the input / output transmission of the expression (1). The function is transformed by introducing it into the denominator of the function T (s). Then, the input / output transfer function T (s) represented by the equation (1) can be modified as follows.
T (s) = T ₁ (s) / a {1-T ₁ (s) · T ₂ (s)}
= T ₁ (s) / {1 + a-1-aT ₁ (s) · T ₂ (s)} (3)

Here, when the input / output transfer function T (s) of the expression (1) and the expression (3) is compared, the transfer function T ₂ (s) of the feedback circuit section of the expression (1) is
(1-a) / T ₁ (s) + aT ₂ (s)
If corrected to (2), an input / output transfer function T (s) that can satisfy the condition of equation (2) can be obtained.

Therefore, according to the principle of the equation (2), the transfer functions T ₁ (s) and T ₂ (s) are selected so that the transmission gain is negative feedback less than the forward gain in the entire frequency range, and the desired frequency is selected. A low noise active RC signal processing circuit having characteristics can be configured. As for various circuits of this low noise active RC signal processing circuit, an example using a current control voltage source (CCVS) by a bipolar transistor in the forward circuit section is shown in FIG. 18, and an example using an anti-phase CCVS by an operational amplifier. This is shown in FIG.

The conventional salen-key circuit, multiple feedback circuit, gyrator circuit, and the like cannot realize a circuit configuration that satisfies the condition of the above formula (2), so the low-noise active RC signal processing shown in FIG. In the circuit, CCVS using a bipolar transistor is adopted for the forward circuit section. This transistor CCVS has a grounded base / transistor on the input side and an emitter follower transistor on the output side, and a resistor R ₁ is connected between these transistors. When the CCVS input current is I _i and the output voltage is V _o , the relationship of V _o = R ₁ I _i is established, and the transfer impedance of this CCVS is R ₁ .

The transistor CCVS having such a configuration is easy to obtain a wideband characteristic, and therefore is convenient for application to a high-frequency signal processing circuit that obtains a transmission gain in the entire frequency range. Since the transfer impedance becomes a resistance, T ₁ (s), which is the numerator of the input / output transfer function, can be set as a constant, thereby satisfying the condition of the above equation (2) and the denominator part. By selecting the transfer function, it is possible to obtain a desired frequency characteristic.

Therefore, the active RC signal processing circuit of FIG. 18 has a basic configuration of a filter circuit using a transistor CCVS as a forward circuit in addition to the feedback signal processing circuit of FIG. 17 having the input / output transfer function T (s). Here, the base-base bipolar transistor Q ₁ , the emitter follower bipolar transistor Q _2, and the resistor R ₁ form a transistor CCVS, which forms a forward circuit of a feedback active RC filter circuit. A feedback circuit unit is connected between the input and output of the CCVS. Note that, in the basic circuit configuration of FIG. 18, only the connection relationship with respect to the AC component is shown, and the DC bias for driving the transistor is omitted. The same applies to the basic circuit configuration described below.

  In the low noise active RC signal processing circuit of FIG. 18 described above, in the filter circuit composed of the forward circuit portion and the feedback circuit portion, the transistor CCVS is employed in the forward circuit portion, and the transfer function of the filter circuit is expressed by the equation (2). The transfer gain function of the feedback circuit unit that satisfies the above is selected, and the loop gain is changed so that the transmission gain in the entire frequency range is a negative feedback equal to or less than the forward gain.

  Therefore, in the feedback signal processing circuit shown in FIG. 19, a loop gain is used so that the transmission gain in the entire frequency range is a negative feedback equal to or less than the forward gain by using an anti-phase CCVS by an operational amplifier instead of the transistor CCVS. Has changed. And the noise of the signal processing circuit is reduced by increasing the loop gain for the entire frequency range.

As shown in FIG. 19, the reverse phase CCVS operational amplifier is basically composed of an operational amplifier OP1 and the resistor R _1, resistor R ₁ is connected between the inverting input of the operational amplifier OP1, and the output ing. Since the input signal to the inverting input of the operational amplifier OP1 is supplied, the output becomes a reversed phase with respect to the input, the current-voltage conversion impedance becomes R _1. The operational amplifier can be composed of a MOS transistor.

  In the signal processing circuit shown in FIG. 19, an anti-phase CCVS using an operational amplifier is used for the forward circuit unit, and the transmission gain of the feedback circuit unit is set to be equal to or less than the forward gain over the entire frequency range so as to satisfy the above-described equation (2). An active RC filter circuit having a desired frequency characteristic is realized by changing to a transfer function that attenuates.

International Publication No. 2003/003575 Pamphlet “Configuration of secondary bandpass type active RC filter by negative feedback”, IEICE, 2001 General Conference Proceedings A-1-20 "Low-pass active RC filter based on transistor CCVS" IEICE 2001 Annual Conference Proceedings A-1-21

  The conventional salen key circuit approaches a positive feedback at the pole frequency (center frequency), and the Q element sensitivity is extremely high. In a single-amplifier type circuit using a multiple feedback system, a stable high Q can be realized, but a forward gain including an open-circuit gain of an operational amplifier is obtained at a pole frequency. In the case of a gyrator using a transistor, it is easy to obtain a stable high Q in a high frequency range, but it is difficult to reduce noise because a loop gain approaches a positive feedback at a pole frequency.

  As described above, when a filter circuit based on an active secondary circuit such as a salen key circuit using a positive phase amplifier, a circuit using a single amplifier, or a circuit using a gyrator is configured, in either case, Although it is convenient for obtaining a high Q, it is difficult to keep the noise low because the negative feedback state does not occur at the pole frequency of the circuit, and this noise problem cannot be solved.

  Obtaining a stable high Q in the high frequency range and achieving low noise have not been solved. Therefore, at present, an active RC filter in the high frequency range has not been put into practical use. Actually, a passive coil (chip inductor) must be used to form a filter circuit in a high frequency region, and this passive coil is externally attached. As a result, miniaturization and monolithic IC of various filter circuits, especially in the high frequency range, has become a problem.

  Therefore, according to the feedback signal processing circuit already developed, the various filter circuits including a wide range of inductances can be easily integrated with other circuits, the circuit configuration can be reduced, and the entire frequency can be reduced. An active RC signal processing circuit having a transfer function for changing the loop gain can be provided by configuring the transmission gain in the band to be negative feedback equal to or less than the forward gain, thereby realizing low noise characteristics.

For example, in the feedback signal processing circuit of FIG. 19, if the operational amplifiers OP1 and OP2 are ideal, the transfer impedance Z _T (s) is given by the following equation (4).
Z _T (s) = R ₁ / {1 + R ₁ / R ₀ T (s)} (4)
Here, since it is possible to satisfy the relationship of | Z _T (s) | <R ₁ , the feedback signal processing circuit of FIG. 19 can have a negative feedback configuration. When an RC ladder circuit is used for the feedback transfer function T (s) of the operational amplifier OP2, the feedback signal processing circuit can constitute a low-pass filter circuit or a high-pass filter circuit.

However, if the high-pass filter circuit is configured so that the target transfer impedance Z _T (s) of the feedback signal processing circuit satisfies the above-described | Z _T (s) | <R ₁ relationship, Requires filter characteristics. In this case, there is a problem that a stable high frequency characteristic cannot be obtained in the loop formed by the operational amplifier OP2 and the feedback circuit of the transfer function T (s).

  In view of this, the present invention provides a frequency-dependent transfer characteristic in the forward circuit section, and negatively feeds back in the pass frequency range to attenuate the gain, thereby integrating with other circuits and reducing the circuit configuration. Another object of the present invention is to provide a feedback signal processing circuit that obtains transfer impedance characteristics that can be a high-pass filter or a low-pass filter while realizing low noise characteristics.

  In order to solve the above problems, in the present invention, in a feedback signal processing circuit, a forward circuit that gives a predetermined transfer characteristic to an input signal and outputs it with a predetermined gain, and a negative feedback from the output of the forward circuit to the input signal And a feedback circuit that has a transfer impedance characteristic in which the output of the forward circuit is less than or equal to the predetermined gain in a predetermined frequency range, and the forward circuit is a current-voltage conversion output circuit.

  The current-voltage conversion output circuit includes a grounded base transistor to which the input signal is input and an emitter follower transistor that outputs a voltage, and has a transfer impedance that determines the predetermined gain, or inverts the input signal The first operational amplifier fed back with the transfer impedance that determines the predetermined gain and the second operational amplifier that outputs the voltage given the signal having the predetermined transfer characteristic as a non-inverting input are provided.

  The transfer impedance characteristic of the forward circuit is a predetermined frequency characteristic of a high-pass filter, or the transfer impedance characteristic is a predetermined frequency characteristic of a low-pass filter.

  As described above, in the present invention, the feedback signal processing circuit is configured by the forward circuit unit and the feedback circuit unit, and the forward circuit unit provides the frequency-dependent transfer characteristic to the input signal, and at a predetermined gain. Since the output is negatively fed back in the pass frequency range by the feedback circuit unit, the gain is attenuated. In addition to high Q and low Q element sensitivity, stable high frequency performance An active RC filter circuit that can be easily improved can be configured.

  In addition, the transfer characteristics of the processing circuit can be determined almost by the values of the capacitor and the resistance, which makes it easy to design the signal processing circuit without using the inductance. Can be achieved.

  Next, embodiments of the feedback signal processing circuit of the present invention will be described below with reference to the drawings. First, before describing the embodiments of the present invention, the basics regarding the configuration of the feedback signal processing circuit of the present invention will be described.

The target transfer impedance Z _T (s) of the feedback signal processing circuit shown in FIG. 19 is expressed by the above equation (4). Here, by satisfying the relationship of | Z _T (s) | <R ₁ , the feedback signal processing circuit can have a negative feedback configuration. If an RC ladder circuit is used for the feedback transfer function T (s) of the operational amplifier OP2, the feedback signal processing circuit becomes a low-pass filter circuit or a high-pass filter circuit. However, since a high-pass filter characteristic is required for the feedback circuit section, a stable high-frequency characteristic cannot be obtained in the loop formed by the operational amplifier OP2 and the feedback circuit of the transfer function T (s).

Therefore, in the embodiment of the present invention, if the target transfer impedance Z _T (s) of the feedback signal processing circuit represented by the equation (4) is modified and corrected, and R ₀ · T (s) is set to Z (s). The target transfer impedance Z _T (s) is expressed as the following equation (5).
Z _T (s) = Z (s) / {1 + Z (s) / R ₁ } (5)

Looking at the target transfer impedance Z _T (s) expressed by equation (5), the numerator of the equation is Z (s), which is a transfer function having a frequency-dependent characteristic in the feedforward circuit section. This means that Z (s) should be provided, and a desired frequency characteristic can be obtained by selecting the transfer function of the molecular part. Here, if Z (s) is a function of the same type as the target transfer function, for example, a low-pass filter can be a low-pass filter characteristic function, and a high-pass filter can be a high-pass filter characteristic function.

If the relationship | Z _T (s) | <| Z (s) | is satisfied, it can be seen that the feedback signal processing circuit can stably apply negative feedback in the pass frequency range. That is, even when the forward circuit portion in the feedback signal processing circuit has frequency-dependent characteristics, stable negative feedback is achieved, and low noise characteristics can be ensured. First, in the feedback signal processing circuit according to the present invention, the basic principle that the transmission gain in a predetermined frequency region is negative feedback with a forward gain or less will be described with reference to FIG.

  The feedback signal processing circuit of the present invention employs a form in which a frequency-dependent active RC filter circuit having a predetermined transfer characteristic is inserted in the forward circuit section. The basic configuration of the signal processing circuit is shown in FIG. In the feedback signal processing circuit of FIG. 1, a current control voltage source (CCVS) is employed, and the forward circuit unit is configured by a transistor CCVS taking a bipolar transistor as an example. The output side transistor is connected to the input side transistor to form a feedback circuit section.

The transistor CCVS has a grounded transistor Q ₁ on the input side and an emitter follower transistor Q ₂ on the output side, and an RC filter circuit having a transfer impedance Z (s) is connected between these transistors. Has been. The output of the feedback type signal processing circuit is taken from the resistor R _E, which is connected to the transistor Q _2. The collector terminal of the transistor Q ₂ is connected to the emitter terminal of the transistor Q ₁ to form a feedback circuit section. Therefore, transfer impedance Z _T (s) is the input current of the CCVS I _i, and the output voltage is V _o, V _o = the relationship _{R 1 I i, Z T (} s) = V o / I i The relationship between the transfer impedance Z _T (s) and the transfer impedance Z (s) is expressed by the above equation (5).

The transistor CCVS having such a configuration is easy to obtain a wideband characteristic, and is therefore convenient for application to the high-frequency signal processing circuit of the present invention that obtains transmission gain in the entire frequency range. Then, T ₂ (s), which is the denominator of the input / output transfer function of the feedback signal processing circuit shown in FIG. 17, can be set as a constant, thereby satisfying the condition of the above formula (2) easily. In addition, a desired frequency characteristic can be obtained by selecting the transfer function of the molecular part.

In the present invention, the transfer functions T ₁ (s) and T ₂ (s) are selected according to the principle according to the above equation (5) so that the transmission gain is a negative feedback equal to or less than the forward gain in the predetermined frequency range. A feedback type signal processing circuit having a desired frequency characteristic is configured. Next, with respect to various circuits related to the feedback type signal processing circuit, a first current control voltage source (CCVS) using a bipolar transistor is used as a forward circuit unit. This embodiment is divided into the second embodiment using the anti-phase CCVS by the operational amplifier, and each will be described while showing various specific examples.

[First Embodiment]
In the feedback signal processing circuit according to the first embodiment, a current control voltage source (CCVS) using a bipolar transistor is used in the forward circuit section. In the feedback signal processing circuit, an RC filter circuit having a high-pass filter characteristic is provided. An example of a configuration circuit connected to the forward circuit section is shown in FIG. The feedback signal processing circuit shown in FIG. 2 is based on the signal processing circuit of FIG. 1, and the same parts are denoted by the same reference numerals.

Here, in the feedback signal processing circuit of FIG. 2, an RC filter circuit is connected between the transistor Q ₁ and the transistor Q ₂ constituting the CCVS of the forward circuit section, and the resistors R ₀ , R ₁ , R ₂ and capacitors C ₁ and C ₂ form a secondary ladder-type high-pass filter circuit. In the circuit configuration of FIG. 2, only the connection relationship with respect to the AC component is shown, and the DC bias for driving the transistor is omitted.

Here, assuming that the transistor in the feedback signal processing circuit of FIG. 2 is an ideal type, the transfer impedance Z _T (s) of the secondary high-pass active RC filter circuit shown in FIG. It becomes like 6).
Z _T (s) = V _o / I _i
= 1 / [1 / R _E + 1 / R ₀ + 1 / R ₁ + 1 / R ₂
+ {(1 / R ₀ + 1 / R ₁ ) / sC ₂ R ₂
+ (1 / R ₁ + 1 / R ₂ ) / sC ₁ R ₀ }
+ 1 / s ² C ₁ R ₁ C ₂ R ₂ R ₀ ]
= S ² C ₁ R ₁ C ₂ R ₂ R ₀ / [1 + s {C ₁ (R ₁ + R ₀ )
+ C ₂ (R ₁ + R ₂ )} + s ² C ₁ C ₂ {R ₁ R ₂ + R ₁ R ₀
+ R ₂ R ₀ (1 + R ₁ / R _E )}] (6)

Further, when the polar angular frequency ω ₀ and Q relating to the high-pass filter circuit are obtained, the following equations (7) and (8) are obtained.
ω _p = [C ₁ C ₂ {R ₁ R ₂ + R ₁ R ₀ + R ₂ R ₀ (1 + R ₁ / R _E )}] ^−1/2 (7)
Q = (1 / ω _p ) / {C ₁ (R ₁ + R ₀ ) + C ₂ (R ₁ + R ₂ )}
= [C ₁ C ₂ {R ₁ R ₂ + R ₁ R ₀ + R ₂ R ₀ (1 + R ₁ R _E )}] ^−1/2
/ {C ₁ (R ₁ + R ₀ ) + C ₂ (R ₁ + R ₂ )} (8)

Here, when the angular frequency ω is infinite, the transfer impedance Z _T (s) is obtained as shown in the following equation (9).
Z _T (s) = V _o / I _i
= R ₁ R ₂ R ₀ / {R ₁ R ₂ + R ₁ R ₀ + R ₂ R ₀ (1 + R ₁ / R _E )}
= (1 / R ₀ + 1 / R ₁ + 1 / R ₂ + 1 / R _E ) ⁻¹ (9)
Therefore, from this equation (9), the transfer impedance Z _T (s) in the pass frequency region is smaller than the transfer impedance 1 / (1 / R ₀ + 1 / R ₁ + 1 / R ₂ ) of the forward circuit section. This shows that a negative feedback configuration can be realized.

  Next, the feedback signal processing circuit shown in FIG. 2 is shown in a basic configuration for realizing a secondary high-pass active RC filter circuit. An example of a specific circuit configuration is shown in FIG. The specific circuit configuration in the figure also shows a DC bias circuit for driving the bipolar transistor.

In the secondary high-pass active RC filter circuit of FIG. 3, 2SC1845 is used for the npn bipolar transistor Q ₁ constituting the transistor CCVS, and 2SA992 is used for the pnp bipolar transistor Q ₂ , and the values of capacitors and resistors are as follows.
C ₁ = 120, C ₂ = 120 (unit, pF)
R ₀ = 1.5, R ₁ = 14, R _2a = 20, R _2b = 10, R ₃ = 1.2 (unit, kΩ)
The resistors R _2a and R _2b are equivalent to the parallel connection in the high frequency range, and correspond to the resistor R ₂ in the feedback signal processing circuit of FIG. 2, and R ₂ = 6.7 kΩ.

Here, FIG. 4 shows a simulation result of the secondary high-pass active RC filter circuit of FIG. In the figure, the horizontal axis indicates the frequency, the vertical axis indicates the transfer impedance Z _T , and the result that the cut-off frequency f ₀ = about 180 kHz was obtained. According to this, the present invention can be applied to a photoelectric conversion circuit capable of removing background light with a simple circuit configuration. By simply setting the values of circuit elements such as resistors and capacitors, and using only two high-frequency transistors, a feedback signal processing circuit having low noise and sufficient high-frequency characteristics in the GHz band can be realized. .

  FIG. 5 is a diagram showing another specific circuit configuration of the secondary high-pass active RC filter circuit shown in FIG. In FIG. 2, the transistor CCVS of the forward circuit is composed of bipolar transistors. However, the feedback signal processing circuit of FIG. 5 is basically the same as the feedback signal processing circuit of FIG. Is different from that of a MOS field effect transistor.

In the secondary high-pass active RC filter circuit of FIG. 5, the values of the capacitor and the resistor are as follows.
C ₁ = 120, C ₂ = 120 (unit, pF)
R ₁ = 1.5, R ₂ = 0.5, R ₃ = 14, R ₄ = 10, R ₅ = 20, R ₅ = 0.58 (unit, kΩ)
The resistors R ₄ and R ₅ are equivalent to the parallel connection in the high frequency region, and correspond to the resistor R ₂ in the feedback signal processing circuit of FIG.

Here, FIG. 6 shows a simulation result of the secondary high-pass active RC filter circuit of FIG. In the figure, the horizontal axis indicates the frequency, the vertical axis indicates the transfer impedance Z _T , and the result that the cut-off frequency f ₀ = about 180 kHz was obtained. According to this, with a simple circuit configuration, values of circuit elements such as resistors and capacitors are set as appropriate, and by using high-frequency transistors, a feedback signal processing circuit having sufficient high-frequency characteristics in the GHz band is realized. it can.

[Second Embodiment]
In the feedback signal processing circuit of the first embodiment described above, a current control voltage source (CCVS) using a bipolar transistor is used in the forward circuit section, and an active RC filter circuit having high-pass filter characteristics is connected to the forward circuit section. Although the circuit configuration is the same as in the first embodiment, the basic signal processing circuit according to the second embodiment uses CCVS with bipolar transistors in the forward circuit section, but a low-pass active RC filter circuit is connected. Is different. An example of the circuit configuration is shown in FIG. The feedback signal processing circuit shown in FIG. 7 is based on the signal processing circuit of FIG. 1, and the same parts are denoted by the same reference numerals.

Here, in the feedback signal processing circuit of FIG. 7, resistors R ₀ , R ₁ , R ₂ and capacitors C ₁ , C ₂ are placed between the transistors Q ₁ and Q ₂ constituting the CCVS of the forward circuit section. A second-order ladder-type low-pass filter circuit is formed. The output of the feedback type signal processing circuit is removed from the resistor R _E, which is connected to the transistor Q _2, the collector terminal of the transistor Q ₂ is connected to the emitter terminal of the transistor Q _1, the feedback circuit portion is formed. In the circuit configuration of FIG. 7 as well, only the connection relationship with respect to the AC component is shown, and the DC bias for driving the transistor is omitted.

Here, assuming that the transistor in the feedback signal processing circuit of FIG. 7 is an ideal type, the transfer impedance Z _T (s) of the secondary low-pass active RC filter circuit shown in FIG. It becomes like 10).
Z _T (s) = V _o / I _i
= R ₀ / [1 + R ₀ / R _E + s {C ₁ (R ₁ + R ₀ )
+ C ₂ (R ₁ + R ₂ + R ₀ )} + s ² C ₁ C ₂ R ₂ (R ₁ + R ₀ )] (10)

Further, when the polar angular frequency ω ₀ and Q relating to the low-pass filter circuit are obtained, the following equations (11) and (12) are obtained.
ω _p = {(1 + R ₀ / R _E ) / C ₁ C ₂ R ₂ (R ₁ + R ₀ )} ^−1/2 (11)
Q = (1 / ω _p ) (1 + R ₀ / R _E ) / {C ₁ (R ₁ + R ₀ )
+ C ₂ (R ₁ + R ₂ + R ₀ )}
= {C ₁ C ₂ R ₂ (R ₁ + R ₀ ) (1 + R ₀ R _E )} ^-1/2
/ {C ₁ (R ₁ + R ₀ ) + C ₂ (R ₁ + R ₂ + R ₀ )} (12)

According to the above equation (10), the transfer impedance Z _T (s) in the pass frequency range is smaller than R ₀ which is the transfer impedance of the forward circuit unit, and thus it can be understood that negative feedback can be realized. In the configuration of the secondary low-pass active RC filter circuit shown in FIG. 7, the resistor R ₁ is not essential, and the resistance value may be R ₁ = 0.

  Next, the feedback signal processing circuit shown in FIG. 7 is shown in a basic configuration for realizing a secondary low-pass active RC filter circuit. An example of a specific circuit configuration is shown in FIG. The specific circuit configuration in the figure also shows a DC bias circuit for driving the bipolar transistor.

In the secondary low-pass active RC filter circuit of FIG. 8, 2SC1845 is used for the npn bipolar transistor Q ₁ and 2SA992 are used for the pnp bipolar transistor Q ₂ constituting the transistor CCVS, and the values of capacitors and resistors are as follows.
C ₁ = 30, C ₂ = 30 (unit, pF)
R ₀ = 1.5, R ₂ = 2.0, R ₃ = 1.2, R _E = 0.45 (unit, kΩ)
Note that the resistance R ₁ in the secondary low-pass active RC filter circuit of FIG. 7 has a resistance value of 0, and the resistance R ₀ is connected in parallel to the capacitor C ₁ in the high frequency range.

Here, FIG. 9 shows a simulation result of the secondary low-pass active RC filter circuit of FIG. In the figure, the horizontal axis indicates the frequency and the vertical axis indicates the transfer impedance Z _T , and the result that the cut-off frequency f ₀ = about 5 MHz is obtained, and a satisfactory second-order low-pass active RC filter circuit result is realized. ing. According to this, it can be applied to a low-pass filter circuit for a high-frequency circuit with a simple circuit configuration. The maximum flat characteristic can be obtained by adjusting the value of the ratio between the resistor R ₀ and the resistor R _E. Further, a feedback signal processing circuit having low noise and sufficient high frequency characteristics can be realized by using only two high frequency transistors.

  FIG. 10 is a diagram showing another specific circuit configuration of the secondary low-pass active RC filter circuit shown in FIG. In FIG. 7, the transistor CCVS of the forward circuit is composed of bipolar transistors. However, the feedback signal processing circuit of FIG. 10 is basically the same as the feedback signal processing circuit of FIG. Is different from that of a MOS field effect transistor.

In the secondary low-pass active RC filter circuit of FIG. 10, the values of the capacitor and the resistor are set as follows.
C ₁ = 30, C ₂ = 30 (unit, pF)
R ₁ = 1.5, R ₂ = 2.0, R ₃ = 0.5, R _E = 0.58 (unit, kΩ)
Also in this case, the resistor R ₁ is in the high frequency range, would be connected in parallel with the capacitor C _1, also a resistance R ₁ in the secondary low-pass active RC filter circuit of FIG. 7, The resistance value is 0.

Here, FIG. 11 shows a simulation result of the second-order low-pass active RC filter circuit of FIG. In the figure, the horizontal axis indicates the frequency, the vertical axis indicates the transfer impedance Z _T , and the result that the cutoff frequency f ₀ = about 2.72 MHz was obtained. According to this, with a simple circuit configuration, values of circuit elements such as resistors and capacitors are set as appropriate, and by using a high-frequency transistor, a feedback signal processing circuit having sufficient high-frequency characteristics in the GHz band is realized. it can.

In the secondary low-pass active RC filter circuit shown in FIG. 8, an RC filter circuit is connected between the transistor Q ₁ and the transistor Q ₂ constituting the CCVS of the forward circuit section, and the resistors R ₀ , A secondary ladder-type low-pass filter circuit is formed by R ₂ and R ₃ and capacitors C ₁ and C ₂ . This low-pass filter circuit can be formed by a complete integration circuit.

  FIG. 12 shows a feedback signal processing circuit in which a complete integration circuit is incorporated in a low-pass filter circuit. The feedback signal processing circuit of FIG. 12 is based on the secondary ladder type active RC filter circuit of FIG. 8, and the same parts are denoted by the same reference numerals. In the forward circuit section, a transistor CCVS is configured and an RC filter circuit is connected.

Therefore, in the RC filter circuit in the feedback signal processing circuit of FIG. 12, instead of the subsequent RC circuit constituting the RC filter circuit shown in FIG. 8, that is, the filter circuit by the resistor R ₂ and the capacitor C ₂ , A complete integration circuit including a capacitor C ₂ is incorporated. As shown in FIG. 12, this complete integration circuit is formed by bipolar transistors Q ₁₁ , Q ₁₂ , Q ₁₃ and resistors R ₁₁ , R ₁₂ , R ₁₃ in addition to the capacitor C ₂ . The transistor Q ₁₃ and the resistor R ₁₃ are connected to the voltage source and become a current source for the capacitor C ₂ .

In this complete integration circuit, assuming that the base voltage of the transistor Q ₁₁ , which is the end voltage of the capacitor C ₁ , is V, the end voltage V _C2 of the capacitor C ₂ is
_{V C2 = V / sC 2 R} E
The gain in the high frequency range can be increased.

  According to the low-pass active RC filter circuit using this complete integration circuit, although it is necessary to add three transistors and three resistors, a simple circuit configuration is still possible, and values of circuit elements such as resistors and capacitors are sufficient. By using a high-frequency transistor, a low-noise property can be improved and a feedback signal processing circuit having sufficient high-frequency characteristics in the GHz band can be realized.

[Third Embodiment]
In the first and second embodiments described above, as shown in FIG. 1, a current control voltage source (CCVS) is employed in the feedback signal processing circuit, and a forward circuit of the signal processing circuit. The part is composed of a transistor CCVS by a bipolar transistor or a field effect transistor, and the output side transistor is connected to the input side transistor to form a feedback circuit part.

  Therefore, in the third embodiment, an operational amplifier is used in place of the two transistors constituting the CCVS, and the loop gain is changed so that the transmission gain in the pass frequency region of the forward circuit section becomes negative feedback. I did it. Then, the noise of the signal processing circuit is reduced by increasing the loop gain for the pass frequency range.

  Although the configuration of the anti-phase CCVS by the operational amplifier has been conventionally used, the anti-phase CCVS is basically composed of an operational amplifier OP and a resistor R, and this resistor R is an inverting input of the operational amplifier OP and its output. Connected between. Therefore, ignoring the finite GB product of the operational amplifier OP, an input signal is supplied to the inverting input of the operational amplifier OP, so that the output is in reverse phase with respect to the input, and the current-voltage conversion impedance is R. The operational amplifier OP can be composed of a MOS field effect transistor.

  Next, using the anti-phase CCVS by the operational amplifier, the transmission gain is changed to a transfer function that attenuates below the forward gain over the pass frequency range so as to satisfy the above equation (2), and the active function having the desired frequency characteristic is obtained. The implementation of the RC filter circuit will be described separately for each of the high-pass and low-pass filter circuits.

(High-pass active RC filter circuit)
A specific example of the secondary high-pass active RC filter circuit using the anti-phase CCVS by the operational amplifier is shown in FIG. In the filter circuit, instead of the transistor Q _{1 in} FIG. 2, an operational amplifier OP 1 having a resistor R ₀ connected between the inverting input terminal and the output terminal is arranged, and instead of the transistor Q ₂ , an inverting input terminal and An operational amplifier OP2 connected to the output terminal is arranged.

A high pass RC filter circuit having the same configuration as the secondary ladder RC filter circuit shown in FIG. 2 is connected between the output terminal of the operational amplifier OP1 and the non-inverting terminal of the operational amplifier OP2. The operational amplifier OP1, the RC filter circuit, and the operational amplifier OP2 form a forward circuit portion of the feedback signal processing circuit. Further, a parallel circuit of a resistor R ₃ and a capacitor C ₃ is connected between the output terminal of the operational amplifier OP2 and the inverting input terminal of the operational amplifier OP1, thereby forming a feedback circuit section.

The transfer impedance function Z _T (s) of the secondary high-pass active RC filter circuit of FIG. 13 is expressed by the following equation (13) assuming that each operational amplifier is an ideal type.
Z _T (s) = V _o / I _i
= −s ² C ₁ C ₂ R ₁ R ₂ R ₀ / {1 + s (C ₁ R ₁ + C ₂ R ₂ + C ₂ R ₁ )
+ S ² C ₁ C ₂ R ₁ R ₂ (1 + R ₀ / R ₃ )} (13)

In the secondary high-pass active RC filter circuit of FIG. 13, the values of the capacitor and the resistor are as follows.
C ₁ = 50, C ₂ = 50 (unit, pF)
R ₀ = 20, R ₁ = 20, R ₂ = 20, R ₃ = 5 (unit, kΩ)

FIG. 14 shows a simulation result of the high-pass active RC filter circuit using the operational amplifier of FIG. In the figure, the horizontal axis indicates the frequency and the vertical axis indicates the transfer impedance Z _T , and the result that the cutoff frequency f ₀ = 70 kHz was obtained. This shows that a high-pass active RC filter circuit can be realized with a simple circuit configuration. By appropriately setting the values of circuit elements such as resistors and capacitors, and using only two operational amplifiers, stable characteristics can be obtained in a high frequency range as compared with the high-pass active RC filter circuit of FIG. it can.

(Low-pass active RC filter circuit)
A specific example of a secondary low-pass active RC filter circuit using an anti-phase CCVS by an operational amplifier is shown in FIG. In the filter circuit, instead of the transistor Q _{1 in} FIG. 7, an operational amplifier OP 1 having a resistor R ₀ connected between the inverting input terminal and the output terminal is arranged, and instead of the transistor Q ₂ , an inverting input terminal and An operational amplifier OP2 connected to the output terminal is arranged.

A low-pass RC filter circuit having the same configuration as the secondary ladder RC filter circuit shown in FIG. 7 is connected between the output terminal of the operational amplifier OP1 and the non-inverting terminal of the operational amplifier OP2. The operational amplifier OP1, the RC filter circuit, and the operational amplifier OP2 form a forward circuit portion of the feedback signal processing circuit. Furthermore, between the inverting input terminal of the output terminal and the operational amplifier OP1 of the operational amplifier OP2, a resistor R ₃ is connected, the feedback circuit portion is formed.

The transfer impedance function Z _T (s) of the secondary low-pass active RC filter circuit of FIG. 15 is expressed by the following equation (14) assuming that each operational amplifier is an ideal type.
Z _T (s) = V _o / I _i
= −R ₀ / {1 + R ₀ / R ₃ + s (C ₁ R ₁ + C ₂ R ₂ + C ₂ R ₁ )
+ S ² C ₁ C ₂ R ₁ R ₂ } (14)

In the secondary low-pass active RC filter circuit of FIG. 15, the values of the capacitor and the resistor are as follows.
C ₁ = 120, C ₂ = 120 (unit, pF)
R ₀ = 20, R ₁ = 20, R ₂ = 20, R ₃ = 5 (unit, kΩ)

FIG. 16 shows a simulation result of the low-pass active RC filter circuit using the operational amplifier of FIG. In the figure, the horizontal axis indicates the frequency, the vertical axis indicates the transfer impedance Z _T , and the result that the cutoff frequency f ₀ = about 160 kHz was obtained. This shows that a low-pass active RC filter circuit can be realized with a simple circuit configuration. By appropriately setting the values of circuit elements such as resistors and capacitors, and using only two operational amplifiers, reliable attenuation characteristics were obtained even in a high frequency range from 10 ⁷ Hz to 10 ⁹ Hz.

  As described above, according to the secondary ladder type active RC filter circuit according to the first to third embodiments, the RC filter circuit is incorporated in the forward circuit portion of the signal processing circuit, and the forward circuit portion has a predetermined gain. The CCVS is provided, and the feedback circuit unit negatively feeds back the forward circuit output in the pass frequency range, so that the noise can be easily reduced. In addition, the transfer characteristics of the feedback signal processing circuit can be determined almost by the values of the capacitor and resistance, making it easy to design the signal processing circuit without using inductance, and reducing the size of the processing circuit. High integration can be achieved.

  In the above-described embodiment, the RC filter circuit incorporated in the forward circuit unit has been described by taking a second-order ladder shape as an example. However, the RC filter circuit is not limited to the second-order ladder shape, and is a multistage filter having a third or higher order. A feedback signal processing circuit of the present invention can be realized by incorporating a circuit. Further, the RC filter circuit incorporated in the forward circuit section is not limited to a ladder type, and other RC filter circuits in which a resistor and a capacitor are appropriately connected can be adopted, and not only a high pass filter and a low pass filter but also a band pass A filter can also be realized.

It is a figure which shows the basic composition of the feedback type signal processing circuit which connected the frequency dependence circuit to the forward part. It is a figure which shows the circuit structure of the secondary high-pass active RC filter circuit by 1st Embodiment. FIG. 3 is a diagram illustrating a specific circuit configuration of the secondary high-pass active RC filter circuit of FIG. 2. It is a figure which shows the result of having simulated the frequency-transfer impedance characteristic in the secondary high-pass active RC filter circuit of FIG. FIG. 3 is a diagram showing another specific circuit configuration of the secondary high-pass active RC filter circuit of FIG. 2. It is a figure which shows the result of having simulated the frequency-transfer impedance characteristic in the secondary high-pass active RC filter circuit of FIG. It is a figure which shows the circuit structure of the secondary low-pass active RC filter circuit by 2nd Embodiment. It is a figure which shows the specific circuit structure of the secondary low-pass active RC filter circuit of 2nd Embodiment. It is a figure which shows the result of having simulated the frequency-transfer impedance characteristic in the secondary low-pass active RC filter circuit of FIG. It is a figure which shows the other specific circuit structure of the secondary low-pass active RC filter circuit of 2nd Embodiment. It is a figure which shows the result of having simulated the frequency-transfer impedance characteristic in the secondary low-pass active RC filter circuit of FIG. It is a figure which shows the specific circuit structure at the time of applying a perfect integration circuit in the secondary low-pass active RC filter circuit of 2nd Embodiment. It is a figure which shows the specific circuit structure of the secondary high-pass filter current voltage converter circuit of 3rd Embodiment using an operational amplifier. It is a figure which shows the result of having simulated the frequency-transfer impedance characteristic in the secondary high pass filter current-voltage conversion circuit of FIG. It is a figure which shows the specific circuit structure of the secondary low-pass filter current-voltage conversion circuit of 4th Embodiment using an operational amplifier. It is a figure which shows the result of having simulated the frequency-transfer impedance characteristic in the secondary low-pass filter current-voltage conversion circuit of FIG. It is a figure which shows the basic block diagram of a feedback type signal processing circuit. It is a figure which shows the basic circuit structure of the feedback type signal processing circuit which used the transistor current control voltage source for the forward part. It is a figure which shows the basic block diagram of the feedback type signal processing circuit using an operational amplifier.

Explanation of symbols

_{Q 1, Q 2, Q 11} ~Q 13 bipolar transistors M _1, M ₂ field effect transistors _{R 0 ~R 6, R 11 ~R} 13, R E resistance C ₁ -C ₃ capacitor OP1, OP2 operational amplifier

Claims (6)

A forward circuit that gives a predetermined transfer characteristic to an input signal and outputs the input signal with a predetermined gain;
A feedback circuit for performing negative feedback from the output of the forward circuit to the input signal;
With
A feedback signal processing circuit characterized in that the output of the forward circuit has a transfer impedance characteristic that is less than or equal to the predetermined gain in a predetermined frequency range.   The feedback signal processing circuit according to claim 1, wherein the forward circuit is a current-voltage conversion output circuit.   3. The current-voltage conversion output circuit includes a grounded base transistor to which the input signal is input and an emitter follower transistor that outputs a voltage, and has a transfer impedance that determines the predetermined gain. Feedback type signal processing circuit.   The current-voltage conversion output circuit uses the input signal as an inverting input, and outputs a voltage as a first operational amplifier fed back with a transfer impedance that determines the predetermined gain, and a signal given the predetermined transfer characteristic as a non-inverting input. The feedback signal processing circuit according to claim 2, further comprising two operational amplifiers.   The feedback signal processing circuit according to claim 1, wherein the transfer impedance characteristic is a predetermined frequency characteristic of a high-pass filter.   The feedback signal processing circuit according to claim 1, wherein the transfer impedance characteristic is a predetermined frequency characteristic of a low-pass filter.

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