WO2014080586A1

WO2014080586A1 - Variable-gain amplifier and tuner system equipped with same

Info

Publication number: WO2014080586A1
Application number: PCT/JP2013/006571
Authority: WO
Inventors: 晋一朗上村; 貴文那須; 克昌土方; 錠二林
Original assignee: パナソニック株式会社
Priority date: 2012-11-22
Filing date: 2013-11-07
Publication date: 2014-05-30
Also published as: JPWO2014080586A1

Abstract

This variable-gain amplifier is equipped with: a phase correction circuit (20) for adjusting the phase of an input signal; an amplifier (10) which has a variable gain function and amplifies the signal having the phase which has been adjusted by the phase correction circuit (20); and a control circuit (30) which, when the gain of the amplifier (10) is to be changed, changes the gain in accordance with a gain setting signal (SC1) for setting a gain and controls the amount of phase adjustment by the phase correction circuit (20) in accordance with a phase adjustment signal (SC2) which corresponds to the gain to be set.

Description

Variable gain amplifier and tuner system including the same

The present invention relates to a receiver used in a communication system or a broadcasting system, and relates to a variable gain amplifier that requires low noise characteristics and low distortion characteristics.

Wideband low-noise amplifiers used in radio reception systems such as TV tuners have a wide variable gain range. When the electric field of the received signal is weak, the gain is increased to increase sensitivity, while the electric field of the received signal is strong. In some cases, the gain is lowered to increase the distortion characteristic of the saturated signal. For such gain control, automatic gain control (Auto-Gain Control: hereinafter referred to as AGC) is used so that the output level is constant.

Generally, the gain of the variable amplifier is controlled by changing parameters such as the attenuation of the attenuator inserted in the input or output of the amplifier, the parallel number of the amplifier, and the bias current. In the variable amplifier, in order to increase the variable gain range, it is necessary to change these parameters greatly. However, when these parameters are changed greatly to change the gain of the variable amplifier, the phase of the output of the amplifier is greatly rotated, and the carrier-to-noise ratio (Carrier Noise Ratio: C) of the entire receiver using the amplifier. (N ratio) deteriorates.

In a radio reception system that receives a signal of a Japanese terrestrial digital television broadcasting service (ISDB-T: Integrated Services Digital Broadcasting-Terrestrial), a bandwidth of a frequency of 470 MHz to 770 MHz is used, and an orthogonal frequency division multiplexing is used as a transmission channel encoding method. (OFDM: Orthogonal Frequency-Division Multiplexing). The modulation method is 64QAM, which requires a wide variable gain range and seamless gain change. In order to obtain a good C / N ratio, it is necessary to suppress the phase shift when changing the gain. For example, a tuner system that receives the ISDB-T signal needs to suppress a phase shift within ± 3 °. In addition, a seamless gain change is required even in a mobile terminal in which the radio wave state constantly changes.

Patent Document 1 discloses a technique for suppressing phase rotation. Specifically, the bias of the terminal of the transistor is changed so that the amplitude-phase modulation conversion having the opposite algebraic code occurs with respect to the phase shift caused by the amplifier. In this technique, the bias current of the amplifier is changed by changing the bias of the terminal of the transistor, and the phase shift of the output signal caused by the amplifier is suppressed.

JP 60-157305 A

However, in order to obtain a wide variable gain range using a technique for changing the bias current for phase adjustment (for example, Patent Document 1), it is necessary to greatly change the bias current. Since the transconductance changes due to the change in the bias current, an amplifier gain error occurs, making it difficult to perform automatic gain control of the amplifier. In addition, the above-described change in transconductance may cause distortion in the amplifier, which may degrade the interference characteristics of a reception system using the amplifier. Furthermore, when adjusting the phase by increasing the bias current, there arises a problem that the power consumption of the amplifier itself increases.

In view of the above problems, an object of the present invention is to suppress a phase shift of an output signal of a variable gain amplifier even when a seamless gain change is performed in a variable gain amplifier that requires a wide variable gain range. .

In the first aspect of the present invention, a variable gain amplifier includes a phase correction circuit that adjusts a phase of an input signal, an amplifier that has a variable gain function, amplifies the signal adjusted in phase by the phase correction circuit, and a gain. A control circuit for setting a gain of the amplifier by a gain setting signal for setting a gain and controlling a phase adjustment amount by the phase correction circuit by a phase adjustment signal according to the gain to be set. Yes.

According to this aspect, when the gain of the amplifier is changed, the control circuit sets the gain of the amplifier by the gain setting signal and outputs the phase adjustment signal corresponding to the gain to be set to the phase correction circuit. Controls phase adjustment. As a result, when the gain of the amplifier is changed, the control circuit controls the amount of phase adjustment of the input signal by the phase correction circuit according to the changed gain, so that the phase error (phase shift generated when the gain changes) ) Can be controlled to be canceled by the phase correction circuit. Therefore, even when the gain is changed seamlessly, the phase shift of the output signal of the variable gain amplifier can be kept small. Further, since the phase correction circuit can finely adjust the gain, finer gain setting is possible.

In the second aspect of the present invention, the tuner system includes the variable gain amplifier described in the first aspect.

According to this aspect, since the tuner system includes the variable gain amplifier described in the first aspect, the phase error can be suppressed to a small value and a good carrier-to-noise ratio can be obtained.

According to the present invention, in a variable gain amplifier that requires a wide variable gain range, even when a seamless gain change is performed, the phase error before and after the gain switching can be suppressed to be small, and the finer Gain setting is also possible. Thereby, a good carrier-to-noise ratio can be obtained in a system using this variable gain amplifier.

1 is a circuit diagram illustrating a configuration example of a variable gain amplifier according to a first embodiment. FIG. It is a circuit diagram which shows the other structural example of the variable gain amplifier which concerns on 1st Embodiment. It is a circuit diagram which shows the other structural example of the variable gain amplifier which concerns on 1st Embodiment. It is a circuit diagram which shows the other structural example of the variable gain amplifier which concerns on 1st Embodiment. It is a figure which shows an example of a variable capacity | capacitance. It is a circuit diagram which shows the other structural example of the variable gain amplifier which concerns on 1st Embodiment. It is a figure which shows an example of a variable resistance. It is a figure which shows the structural example of the general variable gain amplifier which has an amplifier of a common source type. It is a figure which shows the small signal equivalent circuit of the variable gain amplifier of FIG. It is a figure which shows the small signal equivalent circuit of the variable gain amplifier of FIG. 7 is a diagram in which the phase shift amount of the variable gain amplifier when changing the gain of the amplifier in the variable gain amplifier of FIG. 6 is compared with and without phase adjustment. It is a circuit diagram which shows the other structural example of the variable gain amplifier which concerns on 1st Embodiment. It is a circuit diagram which shows the other structural example of the variable gain amplifier which concerns on 1st Embodiment. It is a circuit diagram which shows the other structural example of the variable gain amplifier which concerns on 1st Embodiment. It is a circuit diagram which shows the other structural example of the variable gain amplifier which concerns on 1st Embodiment. It is a circuit diagram which shows the other structural example of the variable gain amplifier which concerns on 1st Embodiment. It is a circuit diagram which shows the structural example of the variable gain amplifier which concerns on 2nd Embodiment. It is a circuit diagram which shows the other structural example of the variable gain amplifier which concerns on 2nd Embodiment. It is a circuit diagram which shows the other structural example of the variable gain amplifier which concerns on 2nd Embodiment. In the variable gain amplifier of FIG. 19, the phase shift amount of the variable gain amplifier when changing the gain of the amplifier is compared with or without phase adjustment. It is a figure which shows the example which applied the variable gain amplifier which concerns on each embodiment to the tuner system.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, similar elements are denoted by the same reference numerals, and detailed description thereof is omitted.

<First Embodiment>
FIG. 1 is a circuit diagram showing a configuration example of a variable gain amplifier according to the first embodiment. As shown in FIG. 1, the variable gain amplifier includes an amplifier 10, a phase correction circuit 20, and a control circuit 30 that are configured to be variable in gain.

The amplifier 10 receives an input signal input from the input terminal IN of the variable gain amplifier via the phase correction circuit 20, amplifies the signal, and outputs the amplified signal to the output terminal OUT of the variable gain amplifier.

The control circuit 30 outputs a gain setting signal SC1 for setting the gain of the amplifier 10 to the amplifier 10, and sets the gain of the amplifier 10 to a desired value. Further, the control circuit 30 outputs a phase adjustment signal SC2 for controlling a phase adjustment amount, which will be described later, to the phase correction circuit 20 in accordance with the gain set in the amplifier 10.

The phase correction circuit 20 adjusts the phase of the signal received from the input terminal IN based on the phase adjustment signal SC2 received from the control circuit 30, and outputs the phase adjusted signal to the amplifier 10.

The control circuit 30 may obtain the phase adjustment signal SC2 corresponding to the gain set in the amplifier 10 each time, or hold a table indicating the correspondence between the gain set in the amplifier 10 and the phase adjustment signal SC2 in advance. The phase adjustment signal SC2 corresponding to the gain set in the amplifier 10 may be read from this table.

(Phase correction circuit)
2 to 4 are circuit diagrams showing other configuration examples of the variable gain amplifier according to the first embodiment. More specifically, it is a diagram illustrating an example of the configuration of the phase correction circuit 20.

In FIG. 2, the phase correction circuit 20 includes a variable capacitor 21 connected between the input unit of the amplifier 10 and the ground. The phase correction circuit 20 adjusts the phase of the input signal by changing the capacitance value of the variable capacitor 21 based on the phase adjustment signal SC2 from the control circuit 30. The signal whose phase is adjusted by the phase correction circuit 20 is input to the amplifier 10 and amplified.

In FIG. 3, the phase correction circuit 20 includes a variable capacitor 22 connected between the input terminal IN of the variable gain amplifier and the input terminal of the amplifier 10. The phase correction circuit 20 receives the phase adjustment signal SC2 from the control circuit 30, and adjusts the phase of the input signal by changing the capacitance value of the variable capacitor 22 based on the phase adjustment signal SC2.

In FIG. 4, the phase correction circuit 20 includes a variable capacitor 23 as a first variable capacitor connected between the input terminal IN of the variable gain amplifier and the input terminal of the amplifier 10, the input terminal of the amplifier 10, and the ground. And a variable capacitor 24 as a second variable capacitor connected between the two. The phase correction circuit 20 receives the phase adjustment signal SC2 from the control circuit 30 and changes the capacitance value of at least one of the

variable capacitors

23 and 24 based on the phase adjustment signal SC2 to be input to the amplifier 10. Adjust the phase of the signal to be output.

FIG. 5 is a diagram showing an example of the variable capacitor 21. As shown in FIG. 5, the variable capacitor 21 includes n capacitive elements 80-1 to 80-n (n is an integer of 2 or more) connected in parallel, and capacitive elements 80-1 to 80-n. Transistor switches 81-1 to 81-n serving as second switches are connected in series and receive the phase adjustment signal SC2 at their gates. The phase adjustment signal SC2 has a bus width n, and the corresponding phase adjustment signal SC2 (SC2 <1> to SC2 <n>) is input to each of the transistor switches 81-1 to 81-n. The transistor switches 81-1 to 81-n are turned on / off based on the phase adjustment signal SC2, thereby adjusting the capacitance value of the variable capacitor 21. More specifically, in the transistor switches 81-1 to 81-n, the capacitance value increases by increasing the number of transistor switches to be turned on, while the capacitance value decreases by decreasing the number of transistor switches to be turned on. With the variable capacitor 21 having such a configuration, discrete phase adjustment values can be set by on / off control of the transistor switches 81-1 to 81-n. The

variable capacitors

22, 23, and 24 can also be realized with the same configuration. Further, the variable capacitors 21 to 24 are not limited to the configuration shown in FIG. 5, but may have other configurations as long as the capacitance value can be varied based on the phase adjustment signal SC2.

(Adjusting the phase for changing the gain of the amplifier)
FIG. 6 is a diagram illustrating a configuration example of a variable gain amplifier having the common source amplifier 10. In FIG. 6, the amplifier 10 includes a source-grounded transistor 11 that receives a signal whose phase is adjusted by the phase correction circuit 20 at a gate, and a variable load resistor 12 as a variable resistor connected between a power source and the drain of the transistor 11. The node between the transistor 11 and the variable load resistor 12 is connected to the output terminal OUT. The amplifier 10 receives the gain setting signal SC1 from the control circuit 30, and adjusts the resistance value of the variable load resistor 12 based on the gain setting signal SC1. In other words, the control circuit 30 changes the gain of the amplifier 10 by changing the resistance value of the variable load resistor 12 of the amplifier 10 by the gain setting signal SC1. As shown in FIG. 7, for example, the variable load resistor 12 includes m resistance elements 82-1 to 82-m (m is an integer of 2 or more) connected in parallel, and each resistance element 82-1 to This can be realized by transistor switches 83-1 to 83-m as first switches which are connected in series with 82-m and receive the gain setting signal SC1 at their gates. Here, the gain setting signal SC1 has a bus width of m, and the corresponding gain setting signal SC1 (SC1 <1> to SC1 <m>) is input to each of the transistor switches 83-1 to 83-m. . Then, the resistance value of the variable load resistor 12 is adjusted by performing on / off control of the transistor switches 83-1 to 83-m based on the gain setting signal SC1. More specifically, in the transistor switches 83-1 to 83-m, the resistance value is decreased by increasing the number of transistor switches to be turned on, while the resistance value is increased by decreasing the number of transistor switches to be turned on. With the variable load resistor 12 having such a configuration, the gain of the amplifier 10 can be set discretely by on / off control of the transistor switches 83-1 to 83-m.

First, in the amplifier as shown in FIG. 6, the phase variation (phase shift) caused by adjusting the variable load resistance will be described.

FIG. 8 is a diagram illustrating an example of a common source amplifier having a variable load resistor. The source grounded amplifier 60 has a source connected to the ground, a drain connected to the output terminal OUT, and a transistor 61 that receives an input signal from the input terminal IN at the gate, and is connected between the power supply and the drain of the transistor 61. The variable load resistor 62 (resistance value is R _L ) and a capacitor 63 (capacitance value is C _L ) connected between the output terminal OUT and the ground.

FIG. 9 is a diagram showing a small signal equivalent circuit of the common-source amplifier 60 shown in FIG. In the small signal equivalent circuit of FIG. 9, the gain of the common-source amplifier 60 can be obtained by Expression (1) and the phase can be obtained by Expression (2).

Here, Rs is a signal source impedance, Cgs is a gate-source capacitance of the transistor 61, Cgd is a gate-drain capacitance of the transistor 61, and gm is a transconductance of the transistor 61. From equation (2), varies the phase of the output of the source-grounded amplifier 60 in accordance with the change of the resistance value R _L of the variable load resistor 62, the amount of change in the resistance value R _L is large, it can be seen that the greater the variation in the phase.

Next, the phase adjustment operation when the gain of the amplifier 10 of the variable gain amplifier shown in FIG. 6 is changed will be described using the small signal equivalent circuit shown in FIG. FIG. 10 shows a small signal equivalent circuit in the case where the phase correction circuit 20 is realized by a capacitance circuit having a variable capacitance to ground (for example, FIG. 2 and FIG. 4). The gain of the variable gain amplifier of FIG. Equation (3) and phase can be obtained from equation (4), respectively. Although not shown in FIG. 6, it is assumed that a capacitive load (capacitance value C _L ) is connected between the output terminal OUT and the ground.

Here, Cvar indicates the capacitance value of the variable capacitance of the phase correction circuit 20 with respect to the ground.

When the control circuit 30 reduces the gain of the amplifier 10 by reducing the resistance value of the variable load resistor 12 by the gain setting signal SC1, the first term on the right side of the equation (4) becomes small, and as a result, the phase becomes small. Therefore, when the gain of the amplifier 10 is lowered by the gain setting signal SC1, the control circuit 30 increases the capacitance value Cvar of the variable capacitance of the phase correction circuit 20 with respect to the ground by the phase adjustment signal SC2. As a result, the second term on the right side of Equation (4) is increased, and the phase can be shifted in the opposite direction to the phase shift when the resistance value of the variable load resistor 12 is decreased. Accordingly, the variable gain amplifier shown in FIG. 6 can suppress the phase shift of the variable gain amplifier even when the resistance value of the variable load resistor 12 is reduced. In addition, since the phase correction circuit 20 is adjusted by the phase adjustment signal SC2 when the gain is lowered by the gain setting signal SC1, the variable gain amplifier can perform the phase shift of the output signal even when the gain of the seamless amplifier is changed. Can be suppressed. At this time, there is no problem of increase in power consumption, gain error, or distortion deterioration.

When the control circuit 30 increases the gain of the amplifier 10 by the gain setting signal SC1, the capacitance value Cvar of the variable capacitance of the phase correction circuit 20 with respect to the ground is reduced by the phase adjustment signal SC2, so that the variable gain amplifier Phase shift can be suppressed.

Here, “when” is “when the gain is lowered” or “when the gain is raised” is preferably, for example, simultaneous. In addition, for example, it is preferable to be within a period until a phase shift of ± 3 ° occurs after the gain of the amplifier 10 is switched. In other words, in the case of the above example, it is preferable that the phase correction circuit 20 is adjusted by the phase adjustment signal SC2 within a period until the phase shift of ± 3 ° occurs after the gain is reduced by the gain setting signal SC1. . However, the “time” period is not limited to the above, and may be set within a range in which the phase shift can be suppressed.

When the capacitance value Cvar of the variable capacitor provided on the ground of the phase correction circuit 20 is changed, the gain of the variable gain amplifier calculated by the equation (3) also changes, but the gain due to the change of the capacitance value Cvar. The impact on is small. Therefore, the influence on the gain of the variable gain amplifier due to the change of the capacitance value Cvar is small.

FIG. 11 shows the phase shift amount (without cal) and the variable load resistance when the gain is changed by controlling only the variable load resistor 12 when the gain of the amplifier 10 is changed in the variable gain amplifier shown in FIG. 12 shows a result of comparison between the phase shift amount (with cal) when the gain is changed by controlling both of the phase shifter 12 and the phase correction circuit 20. In FIG. 11, the horizontal axis (indicated as AGCMODE in the figure) represents the auto gain controller mode (gain control setting mode), and the vertical axis (indicated as ΔPhase in the figure) represents the phase shift amount. For example, the phase shift amount at the time of AGCMODE5 represents the phase shift amount at the time of switching from AGCMODE4 to AGCMODE5. As shown in FIG. 11, the phase shift amount (without cal) when the gain is changed by controlling only the variable load resistor 12 increases as the mode of the auto gain controller increases (particularly in AGCMODEs 8 to 10). It is getting bigger. On the other hand, the phase shift amount (with cal) when the gain is changed by controlling both the variable load resistor 12 and the phase correction circuit 20 is larger than that when only the variable load resistor 12 is controlled. Even if it increases, the phase shift amount of the output signal can be kept small, and the phase shift is within ± 3 °. Further, since the phase correction circuit can finely adjust the gain, finer gain setting is possible.

(Other configuration examples)
12 and 13 are circuit diagrams illustrating other configuration examples of the variable gain amplifier according to the first embodiment. More specifically, FIGS. 12 and 13 are diagrams illustrating other configuration examples of the amplifier 10.

12 includes a source-grounded transistor 13 having a variable transconductance function instead of the transistor 11 of the amplifier 10 in FIG. 6, and includes a load 14 instead of the variable load resistor 12. The control circuit 30 changes the gain by switching the transconductance of the transistor 13 according to the gain setting signal SC1. When the gain of the amplifier 10 is changed by the gain setting signal SC1, the control circuit 30 adjusts the phase by the phase correction circuit 20 by the phase adjustment signal SC2. Thus, the variable gain amplifier shown in FIG. 12 can suppress the phase shift amount due to the change in the gain of the amplifier 10 even when the gain of the amplifier 10 is changed seamlessly. Further, since the phase correction circuit can finely adjust the gain, finer gain setting is possible.

Note that the transconductance of the transistor 13 can be switched, for example, by switching the number of transistors 13 in parallel or by controlling the amount of current flowing through the transistor 13. For example, the transistor 13 is connected between the source of the transistor 13 and the ground. It can also be performed by controlling the resistance value of a variable source resistor (not shown).

FIG. 13 shows an example in which a source degeneration type amplifier is used as the amplifier 10. Compared to FIG. 12, the amplifier 10 includes a transistor 15 instead of the transistor 13 having a variable transconductance function. The amplifier 10 includes a variable source resistor 16 between the source of the transistor 15 and the ground.

The amplifier 10 receives the gain setting signal SC1 from the control circuit 30, and changes the gain by changing the resistance value of the variable source resistor 16 based on the gain setting signal SC1. Further, when the gain of the amplifier 10 is changed by the gain setting signal SC1, the control circuit 30 adjusts the phase by the phase correction circuit 20 by the phase adjustment signal SC2. As a result, the variable gain amplifier shown in FIG. 13 can suppress the phase shift amount of the output signal due to the change in the gain of the amplifier 10 even when the gain of the amplifier 10 is changed seamlessly. Further, since the phase correction circuit can finely adjust the gain, finer gain setting is possible.

The variable gain amplifier shown in FIG. 14 has a variable attenuator 40 having a variable attenuation function between the input terminal IN and the phase correction circuit 20 in addition to the variable gain amplifier in FIG. 1 (denoted as ATT in FIG. 14). It has. The control circuit 30 controls the variable attenuator 40 with a control signal SC3 as an attenuation adjustment signal for adjusting the attenuation.

In the variable gain amplifier of FIG. 14, when the gain of the amplifier 10 is changed by the gain setting signal SC1, the control circuit 30 adjusts the amount of attenuation by the variable attenuator 40 by the control signal SC3 and the phase by the phase adjustment signal SC2. The phase is adjusted by the correction circuit 20. Accordingly, the variable gain amplifier shown in FIG. 14 can suppress the phase shift amount of the output signal due to the change in the gain of the amplifier 10 even when the gain of the amplifier 10 is changed seamlessly as in the above-described embodiment. . Further, since the phase correction circuit can finely adjust the gain, finer gain setting is possible.

In FIG. 14, the variable attenuator 40 is connected between the input terminal IN and the phase correction circuit 20, but is connected between the output unit of the phase correction circuit 20 and the input unit of the amplifier 10. May be. Also in this case, when the gain of the amplifier 10 is changed by the gain setting signal SC1, the control circuit 30 adjusts the amount of attenuation by the variable attenuator 40 by the control signal SC3, and the phase correction circuit 20 by the phase adjustment signal SC2. Adjust the phase with.

The variable gain amplifier shown in FIG. 15 includes a variable feedback circuit 50 between the input and output terminals (between the input and output units) of the amplifier 10 in addition to the variable gain amplifier in FIG. The control circuit 30 controls the variable feedback circuit 50 by the control signal SC4.

In the variable gain amplifier of FIG. 15, when the gain of the amplifier 10 is changed by the gain setting signal SC1, the control circuit 30 controls the variable feedback circuit 50 by the control signal SC4 and the phase correction circuit 20 by the phase adjustment signal SC2. Adjust the phase with. As a result, the variable gain amplifier shown in FIG. 15 can suppress the phase shift amount of the output signal due to the change in the gain of the amplifier 10 even when the gain of the amplifier 10 is changed seamlessly as in the above-described embodiment. . Further, since the phase correction circuit can finely adjust the gain, finer gain setting is possible.

The variable gain amplifier shown in FIG. 16 includes a detection circuit 51 that receives the output signal of the amplifier 10 and detects the level of the output signal in addition to the variable gain amplifier shown in FIG. The detection circuit 51 outputs a detection signal SD1 indicating the level of the detected output signal to the control circuit 30. Based on the detection signal SD1, the control circuit 30 sets the gain of the amplifier 10 using the gain setting signal SC1 and controls the phase correction circuit 20 using the phase adjustment signal SC2. As a result, the control circuit 30 can change the gain and adjust the phase according to the output signal level of the amplifier 10.

<Second Embodiment>
FIG. 17 is a circuit diagram showing a configuration example of a variable gain amplifier according to the second embodiment. The variable gain amplifier shown in FIG. 17 further includes an amplifier 52 as a second amplifier connected between the input terminal IN and the output terminal OUT, as compared with FIG. That is, the amplifier 52, the phase correction circuit 20, and the amplifier 10 are connected in parallel between the input terminal IN and the output terminal OUT. The control circuit 30 performs on / off control of the operation of the amplifier 52 by the control signal SC5. In the present embodiment, it is assumed that the gain of the amplifier 52 cannot be changed, and the variable gain amplifier switches the circuit to be operated from the amplifier 52 to the amplifier 10 and changes the gain of the amplifier 10 by the gain setting signal SC1. It is assumed that the gain of the variable gain amplifier is changed. The circuit to be operated can be switched by, for example, the control signal SC5 and the gain setting signal SC1. Note that the gain of the amplifier 52 cannot be changed. However, the present invention is not limited to this, and an amplifier configured so that the gain can be changed may be used.

The variable gain amplifier shown in FIG. 18 includes a variable attenuator 40 (indicated as ATT in FIG. 18) between the input terminal IN and the phase correction circuit 20 in addition to the variable gain amplifier shown in FIG. Therefore, the amplifier 52, the variable attenuator 40, the phase correction circuit 20, and the amplifier 10 are connected in parallel between the input terminal IN and the output terminal OUT.

In the variable gain amplifier of FIG. 18, when the circuit to be operated is switched from the amplifier 52 to the amplifier 10 to change the gain, the control circuit 30 controls the variable attenuator 40 by the control signal SC3, and by the phase adjustment signal SC2. The phase is adjusted by the phase correction circuit 20. As a result, the variable gain amplifier shown in FIG. 18 can suppress the phase shift amount of the output signal due to the change of the gain of the amplifier 10 even when the gain is seamlessly changed, similarly to the variable gain amplifier shown in FIG. . The circuit to be operated can be switched by, for example, the control signal SC5 and the gain setting signal SC1. Note that the gain of the amplifier 52 cannot be changed. However, the present invention is not limited to this, and an amplifier configured so that the gain can be changed may be used.

(Adjusting the phase for changing the gain of the variable gain amplifier)
The phase adjustment operation according to the second embodiment will be described with reference to FIGS. 19 and 20.

FIG. 19 is a diagram showing a detailed configuration example of the phase correction circuit 20 and the variable attenuator 40 in the variable gain amplifier of FIG. As shown in FIG. 19, the variable attenuator 40 has a variable resistance attenuator 27. The phase correction circuit 20 is connected between a variable capacitor 25 as a first variable capacitor connected between the output terminal of the variable attenuator 40 and the input terminal of the amplifier 10, and between the input terminal of the amplifier 10 and the ground. And a variable capacitor 26 as a second variable capacitor. The rest of the configuration is the same as that of the variable gain amplifier of FIG. 17, and detailed description thereof is omitted here. The variable capacitor 25 and the variable capacitor 26 can also operate as the phase correction circuit 20 and the variable attenuator 40 of the variable attenuator 40.

FIG. 20 shows the phase shift amount of the variable gain amplifier before and after switching the circuit when the gain is changed by switching the circuit to be operated from the amplifier 52 to the amplifier 10 in FIG. FIG. 20 shows an example when the input frequency is 600 MHz. In FIG. 20, “AGCMODE” indicates the mode of the auto gain controller (gain control setting mode), and “with cal” indicates when the phase is adjusted by the phase correction circuit 20 when the circuit to be operated is switched. The phase shift amount is indicated, and “without cal” indicates the phase shift amount when the phase is not adjusted by the phase correction circuit 20 when the circuit to be operated is switched.

First, in the period A in FIG. 20, the circuit to be operated is the amplifier 52, and the amplifier 10 is not operating. Specifically, in period A, the gain is switched by controlling the switch of the variable load resistance of the amplifier 52. In this period A, the phase shift amount (without cal) when the gain is changed by controlling only the variable load resistor increases as AGCMODE increases (particularly AGCMODEs 6 to 7) as shown in FIG. . On the other hand, the phase shift amount (with cal) when the gain is changed by controlling both the variable load resistor of the amplifier 52 and the phase correction circuit 20 is the same as the description in FIG. Is within.

Next, in AGCMODE 8, the control circuit 30 switches the circuit to be operated from the amplifier 52 to the amplifier 10. Therefore, in the period B in FIG. 20, the circuit to be operated is the amplifier 10 and the amplifier 52 is not operating. In this period B, when the phase is not adjusted by the phase correction circuit 20 (without cal), the phase shift amount of the variable gain amplifier at the time of switching from the amplifier 52 to the amplifier 10 (at the time of switching from AGCMODE 7 to 8). Is getting bigger. On the other hand, when the phase is adjusted by the phase correction circuit 20 (with cal), an increase in the phase shift amount of the variable gain amplifier at the time of switching can be suppressed. Specifically, the phase shift can be kept small within ± 3 °.

As described above, even when the gain of the variable gain amplifier is changed by switching the amplifiers connected in parallel, the phase correction circuit 20 adjusts the phase of the signal input to the amplifier 10 after the switching. As a result, the amount of phase shift of the output signal due to the gain change can be kept small. Further, since the phase correction circuit 20 is adjusted by the phase adjustment signal SC2 when the circuit to be operated is switched from the amplifier 52 to the amplifier 10, the phase shift of the output signal is reduced even when the gain of the amplifier is seamlessly changed. Can be suppressed. At this time, there is no problem of increase in power consumption, gain error, or distortion deterioration. Further, since the phase correction circuit can finely adjust the gain, finer gain setting is possible.

Note that the frequency band of the

amplifiers

10 and 52 is particularly 40 MHz or more and 1 GHz or less, so that the phase shift of the output signal can be effectively suppressed. However, the frequency band is 40 MHz or more and is not limited to 1 GHz or less.

Further, in the second embodiment, the example in which the two

amplifiers

10 and 52 are connected in parallel has been described. However, even when three or more amplifiers are connected in parallel, the variable gain amplifier is configured in the same manner. The phase shift amount of the output signal due to the gain change can be suppressed small. More specifically, when a phase correction circuit is provided in front of each amplifier connected in parallel and the circuit to be operated is switched, a phase adjustment signal is transmitted from the control circuit to the phase correction circuit provided in front of the amplifier. What is necessary is just to adjust a phase.

In the second embodiment, the operation of the amplifier 52 is controlled by the control signal SC5. However, both the amplifier 10 and the amplifier 52 may be controlled by using the gain setting signal SC1.

In the first and second embodiments, the signals output from the control circuit 30 can be combined, and the control circuit 30 may control each circuit using one signal.

<Application example>
FIG. 21 is a diagram showing an example in which the variable gain amplifier according to each of the above embodiments is applied to a tuner system.

As shown in FIG. 21, the antenna 90 receives an RF signal, and outputs the received signal to the RF signal processing circuit 91 having the variable gain amplifier according to each of the above embodiments. The RF signal processing circuit 91 adjusts the signal strength of the RF signal received from the antenna 90. The mixer 92 receives the local oscillation signal received from the PLL (Phase Locked Loop) 93 and the RF signal whose signal intensity is adjusted by the RF signal processing circuit 91, converts this RF signal into a baseband signal, and outputs it. To do. The low-pass filter (hereinafter referred to as LPF) removes unnecessary high-frequency components from the baseband signal output from the mixer 92. An analog-to-digital converter (hereinafter referred to as ADC) 95 receives the output signal of the LPF 94, converts it to a digital signal, and outputs it to a DSP (Digital Signal Processor) 96. The DSP 96 performs demodulation processing and the like based on the digital signal received from the ADC 95.

For example, when the RF signal processing circuit 91 has the variable gain amplifier of FIG. 14, the variable attenuator 40 receives a signal input from the antenna 90 to the RF signal processing circuit 91, and the signal output from the amplifier 10 is the RF signal processing. The signal is output from the circuit 91 to the mixer 92. In the example in which the RF signal processing circuit 91 includes the variable gain amplifier shown in FIG. 14, another circuit may be provided between the antenna 90 and the variable attenuator 40 or between the amplifier 10 and the mixer 92. Good. Further, the RF signal processing circuit 91 may have a variable gain amplifier other than that shown in FIG.

In the variable gain amplifier according to each embodiment, the DSP 96 may change the gain of the amplifier 10 and control the phase correction circuit 20 instead of the control circuit 30. Further, the DSP 96 can detect the input signal level of the RF signal based on the digital signal received from the ADC 95, and the input detected by the DSP 96 or the control circuit 30 of the variable gain amplifier according to each embodiment is detected by the DSP 96. The gain of the amplifier 10 may be controlled based on the signal level.

Also, the above embodiments can be used in combination. For example, the detection circuit 51 of FIG. 16 may be applied to the variable gain amplifier shown in FIGS.

According to the present invention, in a variable gain amplifier that requires a wide variable gain range, even when seamless gain change is performed, the phase error before and after the gain switching can be suppressed to a small level, and a good carrier-to-noise can be achieved. A ratio can be obtained. Therefore, it is useful, for example, as a wireless communication receiving system, a TV tuner, a mobile phone terminal, or the like.

10 Amplifier 11 Transistor 12 Variable load resistance (variable resistance)
13 Transistor 15 Transistor 16 Variable source resistance (variable resistance)
20

Phase correction circuit

21, 22 Variable capacitor 23 Variable capacitor (first variable capacitor)
24 variable capacity (second variable capacity)
25 Variable capacity (first variable capacity)
26 Variable capacity (second variable capacity)
27 variable resistance attenuator 30 control circuit 40 variable attenuator 50 variable feedback circuit 51 detection circuit 52 amplifier (second amplifier)
81-1 to 81-n Transistor switch (second switch)
83-1 to 83-m Transistor switch (first switch)
90 antenna 91 RF signal processing circuit 92 mixer 95 ADC (analog-digital converter)
SC1 gain setting signal SC2 phase adjustment signal SC3 control signal (attenuation amount adjustment signal)
SC5 Control signal (gain setting signal)

Claims

A phase correction circuit for adjusting the phase of the input signal;
An amplifier having a variable gain function and amplifying the signal phase-adjusted by the phase correction circuit;
A control circuit for setting a gain of the amplifier by a gain setting signal for setting a gain and controlling a phase adjustment amount by the phase correction circuit by a phase adjustment signal corresponding to the set gain when changing the gain; A variable gain amplifier.
The variable gain amplifier of claim 1, wherein
The phase correction circuit has a variable capacitor connected between the input of the amplifier and the ground,
The variable gain amplifier, wherein the control circuit controls a phase adjustment amount by the phase correction circuit by changing a capacitance value of the variable capacitor according to the phase adjustment signal.
The variable gain amplifier of claim 1, wherein
The phase correction circuit has a variable capacitor that receives the input signal at one end and is connected to the input portion of the amplifier at the other end.
The variable gain amplifier, wherein the control circuit controls a phase adjustment amount by the phase correction circuit by changing a capacitance value of the variable capacitor according to the phase adjustment signal.
The variable gain amplifier of claim 1, wherein
The phase correction circuit includes:
A first variable capacitor having one end receiving the input signal and the other end connected to the input of the amplifier;
A second variable capacitor connected between the input of the amplifier and the ground;
The control circuit controls a phase adjustment by the phase correction circuit by changing a capacitance value of at least one of the first and second variable capacitors according to the phase adjustment signal. amplifier.
The variable gain amplifier of claim 1, wherein
The amplifier includes a transistor that receives the phase-adjusted signal, and a variable load resistor provided at the output of the transistor,
The control circuit changes the gain of the amplifier by changing a resistance value of the variable load resistor according to the gain setting signal.
The variable gain amplifier of claim 1, wherein
The amplifier includes a transistor configured to receive the phase-adjusted signal and change transconductance.
The variable gain amplifier, wherein the control circuit changes a gain of the amplifier by changing a transconductance of the transistor according to the gain setting signal.
The variable gain amplifier of claim 1, wherein
The amplifier includes a transistor that receives the phase-adjusted signal, and a variable resistor provided at a source of the transistor,
The variable gain amplifier, wherein the control circuit changes a gain of the amplifier by changing a resistance value of the variable resistor according to the gain setting signal.
The variable gain amplifier of claim 1, wherein
A variable attenuator that has a variable attenuation function and attenuates the input signal,
The phase correction circuit adjusts the phase of the input or output signal of the variable attenuator,
When the gain is changed, the control circuit sets the gain of the amplifier and controls the phase adjustment amount by the phase correction circuit, and in addition to the attenuation amount of the variable attenuator by an attenuation amount adjustment signal for adjusting the attenuation amount And a variable gain amplifier.
The variable gain amplifier of claim 1, wherein
A feedback circuit connected between the output of the amplifier and the input of the amplifier;
The control circuit controls the feedback circuit in addition to setting the gain of the amplifier and controlling the phase adjustment amount by the phase correction circuit when the gain is changed.
The variable gain amplifier of claim 1, wherein
Between the input part of the phase correction circuit and the output part of the amplifier, one or k (k is an integer of 2 or more) second amplifiers or variable amplifiers connected in parallel are provided. ,
The variable gain amplifier, wherein the control circuit is configured to be able to control which of the amplifier and the second amplifier is operated when a gain is changed.
The variable gain amplifier according to claim 8.
Between the input unit of the variable attenuator and the output unit of the amplifier, one or k (k is an integer of 2 or more) second amplifiers or variable amplifiers connected in parallel are provided. ,
The variable gain amplifier, wherein the control circuit is configured to be able to control which of the amplifier and the second amplifier is operated when the gain is changed.
The variable gain amplifier according to claim 8.
The variable attenuator includes at least one of a variable resistance attenuator and a variable capacitance attenuator.
The variable gain amplifier of claim 1, wherein
The amplifier is configured to be able to set gain discretely, and includes a first switch that switches the discrete gain by on / off control,
The phase correction circuit is configured to be able to set a discrete phase adjustment value, and includes a second switch that switches the discrete phase adjustment value by on / off control,
When the gain is changed, the control circuit changes the gain of the amplifier by turning on and off the first switch by the gain setting signal, and turns on and off the second switch by the phase adjustment signal. A variable gain amplifier that controls phase adjustment by the phase correction circuit.
The variable gain amplifier of claim 1, wherein
A variable gain amplifier characterized in that an input signal of the amplifier is a signal of a digital television broadcasting service, multi-valued by an OFDM modulation method, and a frequency band is 40 MHz or more and 1 GHz or less.
The variable gain amplifier of claim 1, wherein
A variable gain amplifier comprising a MOS transistor.
The variable gain amplifier of claim 1, wherein
A detection circuit for detecting an output signal level of the variable gain amplifier;
The variable gain amplifier, wherein the control circuit sets a gain of the amplifier according to an output signal level detected by the detection circuit.
A tuner system comprising the variable gain amplifier according to claim 1.
The tuner system according to claim 17, wherein
An antenna for receiving an RF signal;
An RF signal processing circuit comprising the variable gain amplifier according to claim 1, wherein the RF signal processing circuit adjusts the signal strength of the RF signal received from the antenna;
A mixer that receives an RF output signal output from the RF signal processing circuit and converts the RF output signal into a baseband signal;
An analog-to-digital converter that receives and converts the baseband signal output from the mixer;
The tuner system, wherein the control circuit changes the gain of the variable gain amplifier based on a signal after digital conversion of the analog-digital converter.