JP2000216652A - Automatic gain controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic gain control amplifier with an improved NF where the NF of the entire circuit can be enhanced without deteriorating communication quality in the case that the amplifier is used for a circuit of a receiver or the like. SOLUTION: The automatic gain control amplifier is provided with 1st and 2nd gain control amplifiers 21, 22, a detection circuit 23 at their output sides, 1st-3rd voltage comparators 24-26, 1st and 2nd changeover means 27, 28 that select a control voltage signal to the 1st and 2nd gain control amplifiers 21, 22 in response to 1st and 2nd changeover means control signals Vsw1.2 and a control circuit 29 that receives a gain increase/decrease discrimination signal Vcomp, 1st and 2nd gain setting voltage signals Vset1.2 and 1st and 2nd DC constant voltage signals Vcons1.2 and outputs the prescribed 1st and 2nd changeover means control signals Vsw1.2. Deterioration in the NF can be suppressed by controlling the gain of the 2nd gain control amplifier 22 when the gain is decreased and controlling the gain of the 1st gain control amplifier 21 when the gain is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control amplifier used in a receiver for wireless communication and the like, and more particularly to an NF (No.
auto gain control amplifier with improved noise figure).

[0002]

2. Description of the Related Art In a radio communication or the like, when the received signal power of a receiver fluctuates with time due to fading or the like, the received signal power is controlled to be constant power to stabilize the demodulation circuit input level. AG for the purpose of
An automatic gain control amplifier called C (Automatic Gain Control) amplifier is used.

FIG. 2 is a block diagram showing a circuit configuration of a conventional general receiver using such an automatic gain control amplifier. 2, 1 is an antenna, 2 is a bandpass filter, 3 is a low noise power amplifier, 4 is a mixer, 5 is an automatic gain control amplifier, and 6 is a demodulation circuit.

According to the receiver shown in FIG. 2, an unnecessary frequency component of a signal received by an antenna 1 is first attenuated by a band-pass filter 2, and a low-noise power amplifier 3
Amplified so as not to deteriorate F. Next, the signal amplified by the low-noise power amplifier 3 is down-converted to an intermediate frequency band with the local signal LO by the mixer 4 and input to the automatic gain control amplifier 5. In the automatic gain control amplifier 5, the gain of the amplifier is controlled so that the output signal power becomes constant with respect to the fluctuation of the input signal power. As a result, the power of the signal input to the demodulation circuit 6 can be stabilized, and stable reception characteristics can be obtained.

FIG. 3 is a block diagram showing an example of a circuit configuration of a conventional general automatic gain control amplifier. In FIG. 3, 7 is a gain control amplifier, 8 is a detection circuit, and 9 is a voltage comparator.

In a conventional automatic gain control amplifier having the configuration shown in FIG. 3, a signal Vout output from a gain control amplifier 7 is input to a detection circuit 8, and the detection circuit 8 detects a detection voltage signal corresponding to the power. Vdet is output.
The detection voltage signal Vdet is input to the voltage comparator 9, and in order to set the output power of the gain control amplifier 7 in the voltage comparator 9, the detection voltage signal Vdet is compared with the reference voltage signal Vref so that Vdet becomes equal to Vref. Control voltage signal V for setting gain G (unit: dB) of gain control amplifier 7 as described above.
cont is output.

In the conventional automatic gain control amplifier as shown in FIG. 3, the controllable power range depends on the variable gain width of the gain control amplifier 7, and the correspondence of the gain G to Vcont is shown in FIG. It will be something like

FIG. 4A shows a control voltage signal Vco.
FIG. 7 is a diagram showing a change in gain G of the gain control amplifier 7 with respect to nt. The horizontal axis represents the voltage of the control voltage signal Vcont, and the vertical axis represents the gain G (dB). Gmax and Gmin represent the maximum gain and the minimum gain of the gain control amplifier 7, respectively, and Vmax.
Is the minimum control voltage required to obtain the maximum gain Gmax,
Vmin indicates a control voltage value necessary to obtain the minimum gain Gmin. (B) is a noise figure N for Vcont.
FIG. 9 is a diagram illustrating a change in F. The horizontal axis is the control voltage signal Vcont
The vertical axis represents the noise figure NF (dB),
Gmax and NFGmin indicate the NF for the maximum gain and the minimum gain of the gain control amplifier 7, respectively.

In a general automatic gain control amplifier,
The increase in the gain G tends to saturate with the increase in the control voltage Vcont, and even when Vcont becomes larger than Vmax, the gain G
Will not increase. The NF depends on the gain G, and the NF tends to increase as the gain G decreases.

On the other hand, in an automatic gain control amplifier having the characteristics shown in FIG. 4, the dynamic range Gv (d
B) is as follows.

Gv = Gmax-Gmin If the dynamic range is required to be greater than Gv, multiple stages of automatic gain control amplifiers having a value equal to or different from Gv shown in FIG. 4 are connected. For example, FIG. As shown by, the configuration is such that the two stages of gain control amplifiers are independently controlled.

In FIG. 5, reference numeral 10 denotes a first gain control amplifier;
11 is a first detection circuit, 12 is a second gain control amplifier, and 13 is a second gain control amplifier.
A detection circuit, 14 is a first voltage comparator, and 15 is a second voltage comparator.

In the automatic gain control amplifier having the configuration shown in FIG. 5, the control method of each of the gain control amplifiers 10 and 12 follows the flow of the signal. First, the power of the output signal Vout1 of the first gain control amplifier 10 is reduced as shown in FIG. In the second gain control amplifier 12, the power of the output signal Vout2 is controlled using Vout1 as an input.

In an automatic gain control amplifier having a configuration as shown in FIG. 5, for example, a control voltage versus gain characteristic and a control voltage versus N of a first gain control amplifier 10 and a second gain control amplifier 12 are shown.
Assuming that the F characteristics are different as shown in FIGS. 6A and 6B, the dynamic range GvT (dB) of the automatic gain control amplifier shown in FIG.
1 Determined by the combination of Vcont2. 6A shows the control voltage versus gain characteristic and control voltage versus NF characteristic of the first gain control amplifier 10, and FIG. 6B shows the control voltage versus gain characteristic and control voltage versus control voltage of the second gain control amplifier 12. NF
FIG. 5 is a diagram showing characteristics and is similar to FIGS. 4A and 4B, respectively.

The first gain control amplifier 10 and the second gain control amplifier 10
The dynamic range Gv1 (d
B) and Gv2 (dB) are as follows.

Gv1 = Gmax1-Gmin1 Gv2 = Gmax2-Gmin2 As shown in FIG. 5, two automatic gain control amplifiers 10 and 12 are connected to each other.
In the case of the stage connection, Vcont1 = Vmax1, Vcont
When 2 = Vmax2, the maximum gain Gmax2 + Gmax1 is obtained.
When cont1 = Vmin1, Vcont2 = Vmin2, minimum gain Gmi
n2 + Gmin1. In this case, the dynamic range is as follows.

GvT = (Gmax2 + Gmax1) − (Gmin2 + Gmin1) = (Gmax2−Gmin2) + (Gmax1−Gmin1) = Gv2 + Gv1 In this way, by using a multi-stage configuration, the dynamic range GvT is made larger than in the case of only one stage. It becomes possible.

[0018]

However, in the conventional automatic gain control amplifier shown in FIG. 5, NFT (dB), which is the noise figure of the entire configuration, is the gain G1 of the first gain control amplifier 10 And the noise figure NF1 and the noise figure NF2 of the second gain control amplifier 12, NFT true = NF1 true + (NF2 true-1) /
G1 antilogarithm NFT (dB) = 10log ₁₀ NFT antilogarithm, and the overall almost NF1 antilogarithm of the first-stage NF (d
B) will be determined.

In the conventional automatic gain control amplifier shown in FIG. 5, first, the gain control of the first stage first gain control amplifier 10 is performed. Therefore, when the overall gain is reduced, G1 (dB) is first reduced. Perform control. NF1
There is a problem that the degradation of (dB) becomes large and the NF of the automatic gain control amplifier as a whole becomes severe, thereby increasing the noise power. And when it is used for the receiver, C / N (Carr
However, there is a problem that communication quality deteriorates due to deterioration of carrier-to-noise ratio (carrier to noise ratio).

On the other hand, if the idea that the overall NF is determined by the NF in the first stage is applied to the receiver having the configuration shown in FIG. 2, the NF of the circuit makes the low-noise power amplifier 3 gain more. By changing the characteristic of the automatic gain control amplifier to NF, the communication quality can be improved.

However, if the gain of the low-noise power amplifier 3 is too large, the power of the input signal to the mixer 4 increases, so that the output power characteristics of the mixer 4 are saturated and the input / output characteristics become nonlinear. However, since a distorted wave is generated, the communication quality is degraded.

Therefore, in order to improve the NF of the circuit using the automatic gain control amplifier, the NF of the automatic gain control amplifier itself is improved instead of increasing the gain of the low noise power amplifier 3 to improve the NF. It is necessary.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and has an object to improve the NF of the entire circuit without deteriorating the communication quality when used in a circuit such as a receiver. It is an object of the present invention to provide an automatic gain control amplifier with improved NF.

[0024]

An automatic gain control amplifier according to the present invention receives an input signal and a first control voltage signal, and
A first gain control amplifier for amplifying the input signal and outputting a previous stage output signal while controlling a gain in accordance with the first control voltage signal; and a first gain control amplifier connected to an output side of the first gain control amplifier, A second gain control amplifier for receiving a signal and a second control voltage signal, amplifying the pre-stage output signal and outputting an output signal while controlling the gain in accordance with the second control voltage signal; A detection circuit connected to the output side of the control amplifier for detecting the output signal and outputting a detection voltage signal according to the power; and a detection circuit connected to the output side of the detection circuit, the detection voltage signal and the first reference voltage. Receiving a signal, comparing the two signals, and outputting a first gain setting voltage signal for setting a gain of the first gain control amplifier so that the detection voltage signal becomes equal to the first reference voltage signal. 1 voltage comparison Is connected to the output side of the detection circuit, and the detection voltage signal and the second reference voltage signal are input, and the two signals are compared so that the detection voltage signal becomes equal to the second reference voltage signal. A second voltage comparator that outputs a second gain setting voltage signal that sets a gain of the second gain control amplifier, and is connected to an output side of the detection circuit;
A third voltage comparator that receives the detection voltage signal and the third reference voltage signal, compares the two signals, and outputs a first or second level gain increase / decrease determination signal; and the first voltage comparator Is connected between the output side of the first gain control amplifier and the input side of the first control voltage signal of the first gain control amplifier.
A gain setting voltage signal, a first switching means control signal, and a first DC constant voltage signal are input, and the first gain setting voltage signal or the first DC constant voltage signal according to the level of the first switching means control signal. And a first switching means for outputting the same as the first control voltage signal to the first gain control amplifier; an output side of the second voltage comparator;
A second gain setting voltage signal, a second switching means control signal, and a second DC constant voltage signal which are connected between the second control voltage signal input side of the gain control amplifier and the second switching voltage signal; A second switching means for selecting the second gain setting voltage signal or the second DC constant voltage signal according to the level of the means control signal and outputting the selected signal as the second control voltage signal to the second gain control amplifier; , The first to third
Connected between an output side of a voltage comparator and an input side of the first switching unit control signal of the first switching unit and the second switching unit control signal of the second switching unit, and The first gain setting voltage signal, the first DC constant voltage signal, the second gain setting voltage signal, and the second DC constant voltage signal are input, and the level of the gain increase / decrease determination signal and the first or second A switching means control circuit for outputting the first and second switching means control signals in accordance with the magnitude of a gain setting voltage signal and the first or second DC constant voltage signal, and increasing a gain for the output signal. When increasing the gain of the first gain control amplifier to the maximum, the gain of the second gain control amplifier is increased after decreasing the gain of the second gain control amplifier. It is characterized in that so as to reduce the gain of the first gain control amplifier after.

According to the automatic gain control amplifier of the present invention, with the above configuration, the first and second voltage comparators provided at the outputs of the first and second voltage comparators for controlling the gains of the first and second gain control amplifiers.
When the gain of the whole amplifier is to be reduced according to the power of the output signal of the second gain control amplifier, which is the output from the automatic gain control amplifier, the gain is changed from the second gain control amplifier using the second switching means. When the gain cannot be completely controlled by the second gain control amplifier, control is performed from a subsequent gain control amplifier so that the gain is further reduced by the first gain control amplifier. Therefore, the gain of the automatic gain control amplifier is reduced. In this case, it is possible to suppress rapid deterioration of the NF.

When the gain of the whole amplifier is to be increased, the gain is increased from the first gain control amplifier, and when the gain cannot be completely controlled by the first gain control amplifier, the gain is further increased by the second gain control amplifier. Since control is performed from the gain control amplifier in the preceding stage as described above, it is possible to enhance the effect of improving NF when increasing the gain of the automatic gain control amplifier.

[0027]

As described above, the automatic gain control amplifier of the present invention increases the gain of the output signal by increasing the gain of the first gain control amplifier to the maximum value. Increase the gain of the gain control amplifier,
In the case of decreasing the gain, the gain of the second gain control amplifier is reduced to a minimum, and then the automatic gain control is performed for the entire amplifier so as to reduce the gain of the first gain control amplifier. In the above configuration, the first DC constant voltage signal sets the gain of the first gain control amplifier to be maximum, and the second DC constant voltage signal minimizes the gain of the second gain control amplifier. The third voltage comparator outputs a first level gain increase / decrease determination signal when the detected voltage signal is smaller than the third reference voltage signal, and outputs a second level gain increase / decrease determination signal when the detected voltage signal is larger than the third reference voltage signal. The first switching means selects the first gain setting voltage signal when the first switching means control signal is at the first level, and selects the first DC constant voltage signal when the first switching means control signal is at the second level. The the switching means the second gain setting voltage signal when said second switching means control signal is the first level,
At the second level, the second DC constant voltage signal is selected,
The switching means control circuit determines that the gain increase / decrease determination signal is a first signal.
And when the first gain setting voltage signal is smaller than the first DC constant voltage signal, the first switching means control signal at the first level and the second switching means control signal at the second level are adjusted to the gain increase / decrease. When the determination signal is at the first level and the first gain setting voltage signal is equal to or higher than the first DC constant voltage signal, the second switching means control signal at the second level and the second switching means control signal at the first level When the gain increase / decrease determination signal is at a second level and the second gain setting voltage signal is larger than the second DC constant voltage signal, the first switching means control signal at a second level and the first level at the first level The second switching means control signal is a first level when the gain increase / decrease determination signal is at the second level and the second gain setting voltage signal is equal to or less than the second DC constant voltage signal. 2 By outputting the second switching means control signals of the bell, and performs automatic gain control as described above.

That is, in the automatic gain control amplifier of the present invention, an input signal and a first control voltage signal are input, and the gain is controlled in accordance with the first control voltage signal while amplifying the input signal to produce a pre-stage output signal. And a first gain control amplifier that outputs the first output signal and the previous output signal and the second control voltage signal, and amplifies the previous output signal while controlling the gain according to the second control voltage signal to output an output signal. A second gain control amplifier, a detection circuit connected to the output side of the second gain control amplifier, for detecting the output signal and outputting a detection voltage signal corresponding to the power of the second gain control amplifier; A reference voltage signal is input, and the two signals are compared to output a first gain setting voltage signal for setting the gain of the first gain control amplifier so that the detection voltage signal becomes equal to the first reference voltage signal. A first voltage comparator, the detection voltage signal and the second reference voltage signal, and comparing the two signals, the second gain control so that the detection voltage signal becomes equal to the second reference voltage signal. A second voltage comparator for outputting a second gain setting voltage signal for setting the gain of the amplifier;
The detection voltage signal and the third reference voltage signal are input;
The two signals are compared, and when the detected voltage signal is smaller than the third reference voltage signal, a gain increase / decrease determination signal of a first level is obtained. When the detected voltage signal is larger than the third reference voltage signal, a second level is obtained. Output the gain increase / decrease determination signal of
A voltage comparator, the first gain setting voltage signal, the first switching means control signal, and a first DC constant voltage signal for maximizing the gain of the first gain control amplifier;
When the switching means control signal is at the first level, the first gain setting voltage signal is selected, and when the first switching means control signal is at the second level, the first DC constant voltage signal is selected. A first switching means for outputting a control voltage signal to the first gain control amplifier; a second DC constant for minimizing the gain of the second gain setting voltage signal, the second switching means control signal, and the second gain control amplifier; When a voltage signal is input and the second switching means control signal is at a first level, the second
The gain setting voltage signal is changed to the second switching means control signal.
A second switching means for selecting the second DC constant voltage signal when the signal is at the level and outputting the selected signal as the second control voltage signal to the second gain control amplifier; the gain increase / decrease determination signal and the first gain setting signal; A voltage signal, the first DC constant voltage signal, the second gain setting voltage signal, and the second DC constant voltage signal are input, the gain increase / decrease determination signal is at a first level, and the first gain setting voltage signal is When the first DC constant voltage signal is smaller than the first DC constant voltage signal, the first switching means control signal at the first level and the second switching means control signal at the second level are used as the first and second gain control signals. When the set voltage signal is higher than the first DC constant voltage signal, the second
The first switching means control signal at the first level and the second switching means control signal at the first level, the gain increase / decrease determination signal is at the second level, and the second gain setting voltage signal is at the second level.
When it is larger than the DC constant voltage signal, the first level of the second level
When the gain increase / decrease determination signal is at a second level and the second gain setting voltage signal is equal to or less than the second DC constant voltage signal, the first switching means controls the switching means control signal and the second switching means control signal at the first level. A switching means control circuit for outputting the first switching means control signal of a level and the second switching means control signal of a second level.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a circuit configuration of an embodiment of the automatic gain control amplifier according to the present invention. In FIG. 1, reference numeral 21 denotes a first gain control amplifier, and 22 denotes a second gain control amplifier.
It is a gain control amplifier.

The first gain control amplifier 21 and the second gain control amplifier 22 receive the input signal and the first and second gain control voltage signals, respectively, and respond to the voltage values of the first and second gain control voltage signals. Amplifying the input signal while controlling the gain by using a transistor, FET, MMI, etc.
C or a combination of a transistor or FET and a variable attenuator using a PIN diode or the like is used. Then, the first gain control amplifier 21, which is the preceding amplifier, amplifies the input signal to the automatic gain control amplifier and outputs the amplified signal to the second gain control amplifier 22 as the previous output signal. Next, the second-stage gain control amplifier 22, which is an amplifier at the subsequent stage, amplifies the output signal at the previous stage and outputs the amplified signal as an output signal from the automatic gain control amplifier.

Reference numeral 23 denotes a detection circuit, which is a second gain control amplifier.
It is connected to the output side of the switch 22 and detects an output signal and outputs a detection voltage signal Vdet having a voltage value corresponding to the power. Reference numeral 24 denotes a first voltage comparator, which is a first reference voltage signal Vre from an external circuit for setting the output power of the first gain control amplifier 21.
f1 and the detection voltage signal Vdet are input, the two signals are compared, and the first gain for setting the gain of the first gain control amplifier 21 so that the detection voltage signal Vdet becomes equal to the first reference voltage signal Vref1. The set voltage signal Vset1 is output. Also,
25 is a second voltage comparator, and similarly a second gain control amplifier.
A second reference voltage signal Vref2 and a detection voltage signal Vdet from an external circuit for setting the output power of 22 are input, and the two signals are compared to make the detection voltage signal Vdet equal to the second reference voltage signal Vref2. Output the second gain setting voltage signal Vset2 for setting the gain of the second gain control amplifier 22 as described above.

Reference numeral 26 denotes a third voltage comparator, which receives a third voltage from an external circuit for setting the gain of the entire automatic gain control amplifier.
The reference voltage signal Vref3 and the detection voltage signal Vdet are input, and the two signals are compared to determine whether the power of the output signal of the automatic gain control amplifier is larger or smaller than the desired output power. When it is smaller than the third reference voltage signal Vref3 (Vdet <Vref3), the first level, for example, H
A level increase / decrease determination signal Vcomp is output. When the detected voltage signal Vdet is larger than the third reference voltage signal Vref3 (Vdet> Vref3), the gain increase / decrease determination signal Vcomp of the second level, for example, the L level voltage value is output. Is output. In addition,
When the detection voltage signal Vdet is equal to the third reference voltage signal Vref3, for example, a gain increase / decrease determination signal Vcomp of an H level voltage value is output.

Reference numeral 27 denotes a first switching means, which is a first switching means control signal Vsw1 and a first gain setting voltage signal Vset1, and a first DC constant of a voltage value which maximizes the gain of the first gain control amplifier 21. When the voltage signal Vconst1 is input and the first switching means control signal Vsw1 is at the first level in accordance with the level of the first switching means control signal Vsw1, the control of the gain of the first gain control amplifier 21 is performed by the first gain setting voltage. A signal Vset1 is selected and used as a first control voltage signal in a first gain control amplifier.
21 to control the gain thereof, and when the first switching means control signal Vsw1 is at the second level, selects the first DC constant voltage signal Vconst1 and uses it as the first control voltage signal.
It outputs to the gain control amplifier 21 and switches whether to maximize the gain. Reference numeral 28 denotes a second switching means. Similarly, a second switching means control signal Vsw2, a second gain setting voltage signal Vset2, and a second DC voltage having a voltage value such that the gain of the second gain control amplifier 22 is minimized. The constant voltage signal Vconst2 is input, and according to the level of the second switching means control signal Vsw2,
When the second switching means control signal Vsw2 is at the first level, the second
To control the gain of the gain control amplifier 22, a second gain setting voltage signal Vset2 is selected and output as a second control voltage signal to the second gain control amplifier 22 to control the gain, thereby controlling the second switching means. When the signal Vsw2 is at the second level, the second DC constant voltage signal Vconst2 is selected and output as a second control voltage signal to the second gain control amplifier 22 to switch whether the gain is minimized.

Reference numeral 29 denotes a control circuit, which is a gain increase / decrease determination signal V
comp, the first gain setting voltage signal Vset1, the first DC constant voltage signal Vconst1, the second gain setting voltage signal Vset2, the second
The DC constant voltage signal Vconst2 is input, and according to these signals, the first and second switching means control signals Vsw
2 is output to the first and second switching means 27 and 28. When the gain increase / decrease determination signal Vcomp is at the first level and the first gain setting voltage signal Vset1 is smaller than the first DC constant voltage signal Vconst1, the first switching means control signal V at the first level is used.
It outputs sw1 and a second switching means control signal Vsw2 at the second level. When the gain increase / decrease determination signal Vcomp is at the first level and the first gain setting voltage signal Vset1 is equal to or higher than the first DC constant voltage signal Vconst1, the second switching means control signal Vsw1 at the second level.
And a second switching means control signal Vsw2 at the first level. When the gain increase / decrease determination signal Vcomp is at the second level and the second gain setting voltage signal Vset2 is larger than the second DC constant voltage signal Vconst2, the first switching means control signal V at the second level
It outputs sw1 and the first level second switching means control signal Vsw2. When the gain increase / decrease determination signal Vcomp is at the second level and the second gain setting voltage signal Vset2 is equal to or less than the second DC constant voltage signal Vconst2, the first switching means control signal Vsw1 at the first level.
And a second switching means control signal Vsw2 at the second level.

With such a configuration, the signal input to the first gain control amplifier 21 is amplified by the first gain control amplifier 21 and the second gain control amplifier 22 while the respective gains are automatically controlled by the respective signals. The output signal amplified to the desired output power is output from the second gain control amplifier 22.

Here, gain control in the automatic gain control amplifier of the present invention will be described. First, as for the first gain control amplifier 21 and the second gain control amplifier 22, for example, between the first gain setting voltage signal Vset1 and the second gain setting voltage signal Vset2 and the gain, FIGS. ), The first gain setting voltage signal Vset1 (corresponding to the first control voltage signal Vcont1) and the second gain setting voltage signal Vset2.
As the gain (corresponding to the second control voltage signal Vcont2) increases, the gain also increases. The first gain setting voltage signal Vset1 (Vcont1) and the second gain setting voltage signal Vset2
As shown in FIGS. 6A and 6B, a first control gain setting voltage signal Vset1 is provided between (Vcont2) and NF.
(Vcont1) second gain setting voltage signal Vset2 (Vcont2
) Increases and NF decreases. The first gain control amplifier 21 and the second gain control amplifier 22 may have the same control voltage-gain characteristic and control voltage-NF characteristic, or may have different characteristics. The detection circuit 23 has, for example, a positive correlation between the input power and the detection voltage signal Vdet such that when the input power increases, the detection voltage signal Vdet also increases in a constant relation.

The first voltage comparator 24 and the second voltage comparator 25
For example, the detection voltage signal Vdet is input to, for example, the minus (-) side, and the first reference voltage signal Vref1 and the second reference voltage signal Vref2, which are the reference for setting the output power, are input to the plus (+) side. The first reference voltage signal Vref1 and the second reference voltage signal Vref2 are set as desired by, for example, dividing the power supply voltage Vcc of the automatic gain control amplifier circuit with a resistor as shown in FIG. Value of the voltage.

Also in the third voltage comparator 26, the detection voltage signal Vdet is, for example, on the minus (-) side, and the third reference voltage signal Vref3, which is a reference for setting the output power of the entire automatic gain control amplifier, is plus. Input to the (+) side.
The third reference voltage signal Vref3 is, for example, a signal having a voltage value obtained by converting desired power of the output signal of the automatic gain control amplifier into a voltage value after passing through the detection circuit 23. This third reference voltage signal Vref3 also has a power supply voltage of the automatic gain control amplifier circuit, for example, as shown in FIG.
A voltage of a desired set value is obtained by a method such as dividing the cc with a resistor.

The first voltage comparator 24 determines that the relationship between the detection voltage signal Vdet and the first reference voltage signal Vref1 is Vdet>
In the case of Vref1, that is, when the output signal power is larger than the setting, the voltage of the first gain setting voltage signal Vset1 is reduced,
As a result, the gain of the first gain control amplifier 21 is reduced to reduce the output signal power. On the other hand, when Vdet <Vref1, that is, when the output signal power is smaller than the setting, the voltage of the first gain setting voltage signal Vset1 is increased, thereby increasing the gain of the first gain control amplifier 21 to increase the output signal power. I do. Thus, the gain of the first gain control amplifier 21 is controlled.

Similarly, for the second gain control amplifier 22, the second voltage comparator 25 outputs the detection voltage signal Vdet and the second
When the relation with the reference voltage signal Vref2 is Vdet> Vref2,
That is, if the output signal power is larger than the setting, the second
The voltage of the gain setting voltage signal Vset2 is reduced, thereby lowering the gain of the gain control amplifier 22 and reducing the output signal power. On the other hand, when Vdet <Vref2, that is, when the output signal power is smaller than the setting, the second control voltage signal Vset2
, Thereby increasing the gain of the second gain control amplifier 22 to increase the output signal power. Thus, the gain of the second gain control amplifier 22 is controlled.

However, the first gain control amplifier 21 and the second
The control of the gain of the gain control amplifier 22 is not always performed or performed at the same time. Instead, the control circuit 19 controls the gain increase / decrease determination signal Vcomp and the first gain setting voltage signal Vset1 and the first DC constant voltage signal Vconst1 as described above.・ Second
Gain setting voltage signal Vset2 / second DC constant voltage signal Vconst2
By controlling the first and second switching means 27 and 28 according to the above, either the first gain control amplifier 21 or the second gain control amplifier 22 controls the gain of the entire automatic gain control amplifier.

The first switching means 27 and the second switching means 28
For example, the first and second switching means control signals Vsw1 and Vsw2 control the gains of the first and second gain control amplifiers 21 and 22 as described above. The voltage to be controlled is represented by a first DC constant voltage signal Vconst1 and a second DC constant voltage signal Vcons.
An operation of switching between t2 and the first gain setting voltage signal Vset1 and the second gain setting voltage signal Vset2 output from the first voltage comparator 24 and the second voltage comparator 25 is performed.

The first switching means 27 and the second switching means
Reference numeral 28 denotes a switch which mechanically switches by the first and second switching means control signals Vsw1 and Vsw2 in addition to the one configured by the electric circuit as described above, and an electronically similar process to the above-mentioned switching. For example, a device that performs the operation may be used.

The first DC constant voltage signal Vconst1 and the second DC constant voltage signal Vconst2 are generated by, for example, dividing the power supply voltage Vcc of the automatic gain control amplifier circuit with a resistor as shown in FIG. To a voltage having a desired set value.

In the gain control of the first gain control amplifier 21 and the second gain control amplifier 22, when the voltage to be controlled is fixed, the gain always becomes constant. FIGS. 6A and 6B
The first DC constant voltage signal Vconst1 is set to a voltage Vmax1 at which the maximum gain is obtained in the first gain control amplifier 21, and the second DC constant voltage signal Vconst2 is set to the second DC constant voltage signal Vconst2. The voltage is set to the voltage Vmin2 at which the minimum gain is obtained in the gain control amplifier 22. When the voltages to be controlled are the first gain setting voltage signal Vset1 (Vcont1) and the second gain setting voltage signal Vset2 (Vcont2), the gain varies according to the respective voltage values. Here, the first
The switching means 27 and the second switching means 28 are connected to the first DC constant voltage signal Vco.
Which of the nst1 / second DC constant voltage signal Vconst2 side or the first gain setting voltage signal Vset1 / second gain setting voltage signal Vset2 side is set by the control circuit 29 as described above. One of them is on the gain setting voltage signal side,
The other is on the DC constant voltage signal side, and neither is on the DC constant voltage signal side or the control voltage signal side at the same time.

As described above, the control circuit 29 determines whether the gain of the automatic gain control amplifier is increasing or decreasing based on the detection voltage signal Vdet, and accordingly, the first switching means 27. It has a function of outputting a first switching means control signal Vsw1 and a second switching means control signal Vsw2 for switching the second switching means 28.

When increasing the gain in the automatic gain control amplifier of the present invention, first, the first switching means control signal Vsw
1, the switching means 27 is set to the first gain setting voltage signal Vset1 side, and the switching means 27 is set by the second switching means control signal Vsw2.
28 is set on the side of the second DC constant voltage signal Vconst2. Thus, the gain control is performed by the first gain control amplifier 21. At this time, the NF of the first gain control amplifier 21 is reduced by increasing the gain of the first gain control amplifier 21 in the first stage, so that the synergistic effect of the gain increase and the NF decrease causes the automatic gain control amplifier as a whole. NF
Will be improved.

If it is necessary to further increase the gain even if the gain of the first gain control amplifier 21 is maximized, the first switching means 27 is switched to the first switching means 27 using the first switching means control voltage signal Vsw1. By setting the second switching means 28 to the second gain setting voltage signal Vset2 using the second switching means control signal Vsw2 to the DC constant voltage signal Vconst1, the gain of the entire automatic gain control amplifier is further increased. Can be.

On the other hand, when decreasing the gain, first, the first switching means 27 is set to the first switching means 27 by the first switching means control signal Vsw1.
The gain setting voltage signal Vset1 is set, and the second switching means 28 is set to the second DC constant voltage signal Vconst2 by the second switching means control signal Vsw2.

Thus, the gain control is performed by the second gain control amplifier.
22. If the gain of the second gain control amplifier 22 is minimum, that is, if it is necessary to further reduce the gain even when the second gain setting voltage signal Vset2 = Vmin2, the first switching means control signal Vsw1 performs the first switching. Means 27 to the first gain control voltage signal Vset1 side;
The second switching means 28 is switched to the second by the switching means control signal Vsw2.
By setting to the DC constant voltage signal Vconst2 side, the gain can be further reduced.

In this case, NF is reduced by first decreasing the gain of the second gain control amplifier 22 at the subsequent stage.
F deteriorates, and NF as an automatic gain control amplifier deteriorates due to a synergistic effect of gain increase and NF deterioration.
However, in comparison with the conventional method in which the gain of the first-stage gain control amplifier is reduced first, the NFT
From the equation (dB), NFT (dB) greatly depends on NF1 (dB) and G1 (dB). Even if NF2 (dB) deteriorates due to a decrease in gain, the effect on NFT (dB) is small. It is possible to suppress the deterioration of the NF of the gain control amplifier as a whole.

Thus, the gain control amplifier is connected in series 2
ADVANTAGE OF THE INVENTION According to the automatic gain control amplifier of this invention of the stage-connected structure, NF degradation, especially the NF degradation when decreasing a gain can be suppressed.

It should be noted that the above is only an example of the embodiment of the present invention, and the present invention is not limited to this. Various modifications and improvements may be made without departing from the gist of the present invention. No problem. For example, in a case where two or more gain control amplifiers are connected in series, a first gain control amplifier is applied to a preceding stage (for example, a first stage) and a second gain control amplifier is applied to a subsequent stage (for example, a last stage). May be.

Specifically, for example, in mobile communication,
If it is considered that the power of the signal transmitted from the base station and the mobile station is constant, if the communication area is wide, if the distance between the base station and the mobile station is short, a large power signal will be received. Receives a small power signal.
Therefore, since the difference in power must be kept constant in the receiver, an AGC amplifier having a larger dynamic range is required. To construct such an AGC amplifier, it is necessary to connect three or more stages of gain control amplifiers in series.

Even in such a case, when the gain of the AGC amplifier is reduced by using the automatic gain control amplifier of the present invention, the NF deterioration is prevented by reducing the gain from the last stage gain control amplifier. It can also be applied to mobile communication in which the communication area is wide.

The first gain setting voltage signal Vset1 (first
Control voltage signal Vcont1) / second gain setting voltage signal Vset2
The relationship between the (second control voltage signal Vcont2) and the gain and NF is the relationship shown in FIGS. 6A and 6B, and the inputs of the first voltage comparator 24 and the second voltage comparator 25 Minus (-) the reference voltage signal Vref1 and the second reference voltage signal Vref2
The detection voltage signal Vdet may be input to the (+) side.

Also, the gain increase / decrease determination signal Vcomp and the first and second switching means control signals Vsw1 and Vsw2 are not limited to DC voltage signals. May correspond to the first and second levels.

Further, the first gain control amplifier 21, the second gain control amplifier 22, the first voltage comparator 24, the second voltage comparator 25,
It goes without saying that the third voltage comparator 26 and the like may be constituted by circuits having the same functions, and the detection circuit 23, the first switching means 27 and the second switching means 28 may be constituted by devices having the same functions. No.

[0060]

As described above, according to the automatic gain control amplifier of the present invention, the detection voltage signal which is the output of the detection circuit connected to the output side of the last stage of the gain control amplifier connected in multiple stages is First and second gain control by comparing with the first to third reference voltage signals and inputting them to first and second voltage comparators for controlling the detected voltage signal to be equal to the first and second reference voltage signals A gain for not only obtaining first and second gain setting voltage signals for controlling the amplifier, but also inputting to a third voltage comparator and comparing with the third reference voltage signal to determine an increase or decrease of the gain of the automatic gain control amplifier. An increase / decrease determination signal is also generated, and the control circuit uses the first and second gain control voltage signals and the first and second DC constant voltage signals to control the gain of the first and second gain control amplifiers based on these signals. First to perform sequential control And the connection state of the second switching means is selected, so that when the gain of the entire automatic gain control amplifier is reduced, the gain control from the second gain control amplifier at the subsequent stage is performed, and when the gain is increased, the gain control from the preceding gain control amplifier is performed. Gain control can be performed.

Thus, according to the present invention, it is possible to control the gain from the succeeding stage gain control amplifier when the gain is reduced, as compared with the case where control is performed from the preceding stage gain control amplifier as in the conventional automatic gain control amplifier. Therefore, significant deterioration of the NF can be suppressed, and the gain can be controlled from the gain control amplifier at the preceding stage when the gain is increased. Therefore, the NF is reduced and the overall NF is reduced by the synergistic effect of the gain increase and the NF decrease. It can be improved, and remarkable deterioration of communication quality when used in a receiver can be suppressed.

As described above, according to the present invention, there is provided an automatic gain control amplifier with improved NF that can improve NF of the entire circuit without deteriorating communication quality when used in a circuit such as a receiver. Could be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of an example of an automatic gain control amplifier according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a circuit configuration of a receiver using an automatic gain control amplifier.

FIG. 3 is a block diagram showing an example of a circuit configuration of a conventional automatic gain control amplifier.

FIGS. 4A and 4B are diagrams showing a change in a gain G with respect to a control voltage signal Vcont and a change in a noise figure NF with respect to the control voltage signal Vcont in a conventional gain control amplifier, respectively.

FIG. 5 is a block diagram showing an example of a circuit configuration of a conventional two-stage connection type automatic gain control amplifier.

6A is a diagram illustrating a control voltage versus gain characteristic and a control voltage versus NF characteristic of a first stage gain control amplifier in a two-stage connection type automatic gain control amplifier, and FIG. 6B is a diagram illustrating a control voltage versus gain of a subsequent stage gain control amplifier. FIG. 4 is a diagram showing characteristics and control voltage versus NF characteristics.

[Explanation of symbols]

 21: first gain control amplifier 22: second gain control amplifier 23: detection circuit 24: first voltage comparator 25: second voltage comparator 26: third voltage comparison Unit 27 First switching means 28 Second switching means 29 Control circuit Vcont1 First control voltage signal Vcont2 Second control voltage signal Vdet Detection voltage signal Vref1 ... First reference voltage signal Vref2... Second reference voltage signal Vref3... Third reference voltage signal Vset1... First gain setting voltage signal Vset2. Signal Vcomp: Gain increase / decrease determination signal Vsw1: First switching means control signal Vsw2: Second switching means control signal Vconst1: First DC constant voltage signal Vconst2: Second DC constant Voltage signal

Claims (1)

[Claims] A first gain control amplifier for receiving an input signal and a first control voltage signal, amplifying the input signal while controlling a gain in accordance with the first control voltage signal, and outputting a pre-stage output signal; An output side of the first gain control amplifier, which receives the pre-stage output signal and the second control voltage signal, and amplifies the pre-stage output signal while controlling a gain in accordance with the second control voltage signal; A second gain control amplifier for outputting an output signal, and a detection circuit connected to the output side of the second gain control amplifier for detecting the output signal and outputting a detection voltage signal corresponding to the power thereof; The detection voltage signal and the first reference voltage signal are input to the output side of the circuit, and the two signals are compared.
A first voltage comparator that outputs a first gain setting voltage signal that sets a gain of the first gain control amplifier so that the detection voltage signal is equal to the first reference voltage signal; Are connected, the detection voltage signal and the second reference voltage signal are input, and the two signals are compared to adjust the gain of the second gain control amplifier so that the detection voltage signal becomes equal to the second reference voltage signal. A second voltage comparator that outputs a second gain setting voltage signal to be set; and a second voltage comparator that is connected to an output side of the detection circuit, receives the detection voltage signal and a third reference voltage signal, and compares both signals. A third voltage comparator that outputs a first level or second level gain increase / decrease determination signal, and an output side of the first voltage comparator and an input side of the first control voltage signal of the first gain control amplifier. Connected between the A gain setting voltage signal, a first switching means control signal, and a first DC constant voltage signal are input, and the first gain setting voltage signal or the first DC constant voltage signal according to the level of the first switching means control signal. And a first switching means for outputting the first control voltage signal to the first gain control amplifier as the first control voltage signal; an output side of the second voltage comparator and the second control voltage of the second gain control amplifier. The second gain setting voltage signal, the second switching means control signal, and the second DC constant voltage signal are inputted between the second gain setting voltage signal, the second switching constant control signal and the second switching means control signal. A second switching means for selecting a second gain setting voltage signal or the second DC constant voltage signal and outputting the selected signal as the second control voltage signal to the second gain control amplifier; Vessel output Connected between the first switching means control signal of the first switching means and the input side of the second switching means control signal of the second switching means,
The gain increase / decrease determination signal and the first gain setting voltage signal / the first DC constant voltage signal / the second gain setting voltage signal / the second DC constant voltage signal are input, and the level of the gain increase / decrease determination signal and A switching unit control circuit that outputs the first and second switching unit control signals according to the magnitude of the first or second gain setting voltage signal and the first or second DC constant voltage signal, When the gain for the output signal is increased, the gain of the second gain control amplifier is increased after increasing the gain of the first gain control amplifier to the maximum, and when the gain of the second gain control amplifier is decreased, the gain of the second gain control amplifier is increased. The gain of the first gain control amplifier is reduced after reducing the gain to the minimum.