JPH07321582A - Logarithmic amplifier circuit - Google Patents

Abstract

PURPOSE:To improve noise figure characteristics and to widen the dynamic range of a logarithmic amplifier circuit by making the gain of the limiting amplifier of an initial stage large. CONSTITUTION:A logarithmic transformation circuit receives input signals Vinput and signals logarithmically transformed by a limiting amplifier part 20 constituted of the serially connected plural stages of the limiting amplifiers 21-26 are detected in a detection part 74, quantized in an AD converter 76 and converted to digital signals Dad. Thereafter, a correction operation is performed by a correction value from a logarithmic correction table 79 in a logarithmic scale correction part 78 and logarithmically transformed signals are outputted. Then, the limiting amplifier 21 for which the gain setting of the initial stage of the limiting amplifier part 20 is turned to be more than 16dB and less than 30dB is provided. By making the gain of the limiting amplifier 21 of the initial stage large, the improvement effect of approximately 4-8dB for the noise figure characteristics is obtained. Thus, the dynamic range of this logarithmic amplifier circuit is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for converting an input signal into a logarithmic compression signal.

[0002]

2. Description of the Related Art As an example of a conventional logarithmic amplifier circuit,
There is a logarithmic amplifier circuit that receives an intermediate frequency signal of a spectrum analyzer and converts it into a logarithmic compressed signal. This example
This will be described with reference to FIGS. 3 (a) and 3 (b). Measurement signal Vinpu
t is an intermediate frequency signal having a constant bandwidth and is, for example, an AC signal of 20 MHz. The configuration of this device is shown in FIG.
As shown in (a), 10-stage limiting amplifiers 51-60
A BPF 72, a detector 74, an AD converter 76,
It is composed of a logarithmic scale correction unit 78 and a logarithmic correction table 79.

The internal structure of the limiting amplifiers 51 to 60 is shown in FIG.
As shown in (b), the amplifier 81 and the limit voltage 82
And an adder 83. This amplifier 81
It is a conditional 10 dB amplifier. The conditional amplifier firstly means that the output level amplified by the amplifier 81 upon receiving the input signal Vin is the limit voltage 82 value (for example, 0.5).
v) In the following cases, it operates as a normal 10 dB amplifier. Secondly, when the output level amplified by the amplifier 81 in response to the input signal Vin is equal to or higher than the limit voltage 82 value, the amplifier 81 is limited in amplification degree and has a constant output level of 0.5v. Becomes The adder 83 adds the output level amplified by the amplifier 81 and the input signal Vin to obtain an output signal Vout. As described above, the limit voltage 82 is a limiting element that determines the upper limit of the output level amplified by the amplifier 81. Also, each limiting amplifier 5
In order to realize the logarithmic conversion function in units of 10 dB, the limit voltage 82 for each of 1 to 60 is, for example, 0.5 v, 1 v, 1.
5v, 2v, 2.5v, 3v, 3.5v, 4v, 4.5
v and 5v. In this way, the limit voltage value is set so as to increase in units of 0.5 V, and a gain of 10 dB is given to each of them, thereby realizing a voltage conversion function close to logarithmic conversion. That is, in this example, the output signal Vout is
This is an example in which a voltage value of 0.5 v is converted with a logarithmic weight of 10 dB steps. Here, 5.0v = 0 dB
And 0.5v = −90 dB. That is,
With 10 stages of serially connected limiting amplifiers 51-60, this amplifier becomes a logarithmic conversion amplifier with a dynamic range of 100 dB.

As a result, the measurement signal Vinput is supplied to the limiting amplifier 51 in the first stage and the limiting amplifier 60 in the final stage.
When output from, the output signal Vcnv becomes an output signal converted into a substantially logarithmic scale. Where BPF72
Is a band-pass filter that is inserted between the 10-stage limiting amplifiers 51 to 60 to filter noise signals outside the band frequency range used by the logarithmic amplifier, and is used for NF improvement. .

The detection unit 74 receives the signal Vcnv converted into the logarithmic scale as described above, detects it as a DC signal, filters it with an LPF (low-pass filter), and then supplies it to the AD converter 76. For the detection here, an envelope detection means having good linearity is used. The AD converter 76 receives the detection signal from the detection unit 74, quantizes it, and converts it into a digital signal D
The ad signal is supplied to the logarithmic scale correction unit 78. The logarithmic scale correction unit 78 receives the digital signal Dad from the AD converter 76 and reads the conversion value corresponding to this Dad value from the logarithmic correction table 79 to realize linearity correction, and externally output this conversion data Doutput. Output to. This correction calculation is
As shown by the curve 92 in FIG. 4, each limiting amplifier has its own curve. Therefore, the correction calculation is for linearly correcting the deviation amount from the ideal logarithmic level 90. At the same time, this correction includes error correction in the detection unit 74 and the AD converter 76 circuit portion. This logarithmic correction table 79
Since the correction value of is different for each product, it is obtained in advance during manufacturing adjustment and stored in the logarithmic correction table 79. Further, since the error at the change point between the curve 92 in FIG. 4 and the curve 92 before and after tends to become large, the gain per error amplifier stage is set to 10
It is set to a low level of dB.

[0006]

As described above, 1
Since the gain of the limiting amplifier per stage is kept as low as 10 dB, it is necessary to connect as many as 10 stages in series in order to obtain a desired gain, resulting in an increase in cost. Also, 100
When the gain becomes as high as dB, the influence of internal noise generated by the first-stage and second-stage limiting amplifiers themselves becomes large. That is, the noise figure (NF) characteristic tends to deteriorate, the S / N at low signal input decreases, and the dynamic range of logarithmic conversion decreases.

Therefore, an object of the present invention is to improve the NF characteristics to reduce the deterioration of the dynamic range, and also to reduce the circuit scale to achieve a low cost configuration.

[0008]

FIG. 1 shows a first solution according to the present invention. In order to solve the above-mentioned problem, the configuration of the present invention is a configuration means for providing the limiting amplifier 21 in which the gain setting of the first stage of the limiting amplification unit 20 exceeds 16 dB and is set to less than 30 dB. As a result, the logarithmic amplification circuit means is provided for improving the NF characteristic of the limiting amplifier 21 in the first stage.

The gain switching section 28 in FIG. 2 represents a second solving means according to the present invention. In order to solve the above problems, in the configuration of the present invention, the gain switching unit 28 that switches the gain setting of the first stage of the limiting amplifier is provided, and the logarithmic correction table 79 that corresponds to each switching of the gain setting of the first stage of the limiting amplifier is provided. It is a constituent means. As a result, the logarithmic amplification circuit means is provided for improving the NF characteristic of the limiting amplifier 21 in the first stage.

FIG. 2 shows a third solution according to the present invention. In order to solve the above-mentioned problem, in the configuration of the present invention, the measurement input signal Vinput or the calibration signal from the variable attenuator 34 is switched, and a switch 32 for supplying the limited amplification unit 20 is provided. A signal generator 36 for outputting the signal level of the switch 32 is provided, receives the signal from the signal generator 36, attenuates it to an arbitrary amount of attenuation, and switches 32
A variable attenuator 34 is provided to supply to one side, receives a calibration start signal, and supplies a known level to the limiting amplification unit 20,
The control unit 38 is provided which controls the series of calibrations for receiving the measured digital signal Dad from the AD converter 76, calculating the logarithmic correction value, and storing it in the logarithmic correction table 79. As a result, the logarithmic amplification circuit means is provided for improving the NF characteristic of the limiting amplifier 21 in the first stage. The calibration start condition is to start the calibration by receiving a calibration start signal start from the outside, or to provide a temperature sensor 42 outside and monitor the temperature from the temperature sensor 42 to detect a change above a desired temperature. When it does, it will be the means to start the calibration. As the connection, the output end of the signal generator 36 is connected to the input end of the variable attenuator 34, the output end of the variable attenuator 34 is connected to one input end of the MUX 32, and the input signal Vinput is input to the other input of the MUX 32. The output end of the MUX 32 is connected to the input end of the limiting amplification unit 20, and the output end of the AD converter 76 is connected to the input end of the control unit 38.

[0011]

By increasing the gain of the limiting amplifier 21 in the first stage, the NF characteristic can be improved. As a result,
The dynamic range of the logarithmic amplifier circuit can be widened. In the second embodiment, by providing the calibration unit 30 and performing calibration at any time, it has the effect of significantly reducing the change over time of the individual limiting amplifiers 21 to 26 of the limiting amplification unit 20 and the logarithmic conversion error associated with the temperature change. is there.

[0012]

【Example】

(Embodiment 1) Embodiment 1 of the present invention has a circuit configuration in which the gain per stage of a logarithmic amplifier circuit is increased and the number of stages connected in series is reduced. This will be described with reference to FIG. The circuit configuration of the present invention has six stages of limiting amplifiers 21 to 21.
26, a BPF 72, a detection unit 74, and an AD converter 76.
And a logarithmic scale correction unit 78 and a logarithmic correction table 79.

The internal structure of each of the limiting amplifiers 21 to 26 is the same as the conventional one. However, the gain of the amplifier 81 shown in FIG. 3B is set to 16 dB, and the total gain of the 6-stage limiting amplifiers 21 to 26 is set to 96 dB. As a result, the limiting amplification unit 20 secures the same gain as the conventional one. Further, the limit voltage 82 value of the amplifier 81 at this time is changed from 0.5v to 0.8v. But,
Since the gain of the limiting amplifier is increased as described above, the output signal Dad has a large deviation amount from the ideal logarithmic level 90 as in the output characteristic 94 shown in FIG. The correction of the increased deviation is performed by the linearity correction means using the correction value of the logarithmic correction table 79, as in the conventional technique. The output data Doutput thus obtained can ensure practical logarithmic conversion accuracy. As described above, the limiting amplifier 2
By changing the gain of 1 to 16 dB, the NF characteristics of the limiting amplifier 21 in the first stage and the limiting amplifier 22 in the next stage, in which the NF characteristic is the dominant factor, can be improved by about 4 to 8 dB.

In the first embodiment, if it is desired to emphasize the improvement of the dynamic range performance rather than the accuracy of the linearity of the logarithmic conversion, the amplifier 81 of the limiting amplifier 21 in the first stage.
It is also possible to further increase only the gain of, for example, 20 dB to improve the NF characteristic. If the gain value is set to be too large, the error in logarithmic conversion becomes large, which is not preferable. This gain value is at most 3
A gain setting of less than 0 dB is suitable, and even if it is more than that, the effect of the NF characteristic is small.

(Embodiment 2) As shown in FIG. 2, Embodiment 2 of the present invention is a circuit in which the gain of the limiting amplifier 21 in the first stage is made variable and a calibration means for calibrating the linearity of logarithmic conversion is provided. This is an example of a case where the dynamic range performance is improved and the linearity of logarithmic conversion is also improved by the configuration. The circuit configuration of the present invention has six stages of limiting amplifiers 21 to 26.
, The first stage gain switching unit 28, the calibration unit 30, and the BPF
72, a detection unit 74, an AD converter 76, a logarithmic scale correction unit 78, and a logarithmic correction table 79.
The calibration unit 30 includes a MUX 32, a variable attenuator 34, a signal generator 36, and a control unit 38. The limiting amplifiers 22 to 26 in the second and subsequent stages, the BPF 72, and the detection unit 7
4 and the operation of the AD converter 76 are the same as those in the first embodiment.

The first-stage limiting amplifier 21 includes a gain switching unit 2
Upon receiving the gain switching signal from 8, the gain of the amplifier 81 is switched to two points of 16 dB and 26 dB, for example. This gain switching should be used by setting a low gain value when measuring the fluctuation of the relative value of the minute input signal level of the measurement target with high accuracy, and conversely, setting a low level minute input signal level close to the measurement limit. When measuring, that is, when measuring with a wide dynamic range, set to a high gain value before use. This allows proper use according to the measurement conditions.

By the way, the larger the gain of the amplifier 81, the more the deviation of the measured value Dad from the ideal logarithmic level 90 shown in FIG. 4 becomes larger. As a result, the conversion error of the output data Doutput after the correction processing is simply performed with the fixed correction value is limited to the limiting amplifiers 21 to 2.
6 is a defect that becomes a large error factor due to changes with time and changes in temperature. Therefore, the second embodiment
Then, the calibration unit 30 is provided as a means for correcting the conversion error due to the change with time and the change in temperature as needed to perform the calibration.

The calibration means will be described. The calibration means of the calibration unit 30 is realized by calibrating the entire logarithmic amplification circuit system in the current circuit state and writing and storing the resulting correction value in the logarithmic correction table 79. Control unit 3
8 receives the calibration start signal start from the outside and starts calibration. Alternatively, a temperature sensor 42 is provided outside, and the temperature from the temperature sensor 42 is monitored to start calibration when a change above a desired temperature is detected. MUX32 is
The input signal for switching between the two input signals is supplied to the limiting amplifier 21 in the first stage at the time of calibration from the variable attenuator 34 side. The signal generator 36 is an oscillator that receives a signal from the control unit 38, stops oscillation during non-calibration, and oscillates during calibration to output a known output level, for example, 0 dBm. The oscillation signal Vosc is supplied to the variable attenuator 34. The variable attenuator 34 receives the attenuation parameter signal from the control unit 38, attenuates the oscillation signal Vosc to a predetermined attenuation amount, and then passes through the MUX 32 to the limiting amplifier 2 of the first stage.
Supply to 1.

The control unit 38 applies the calibration signal and
Upon receiving the output data Dad from the D converter 76, a deviation from the expected value level Vcal of the original logarithmic conversion is obtained, and the correction value Hcal = Vcal / Dad at which this deviation becomes zero corresponds to the logarithmic correction table 79. Write to memory location and save.
This operation is performed at every damping step. By the way, in the logarithmic correction table 79, the first stage limiting amplifier 21
Two channels are provided corresponding to the gain switching of the gain switching unit 28, and the log writing in the memory of the logarithmic correction table 79 is written and saved in the channel of the memory corresponding to this gain.

After the above calibration is completed, the MUX 32 is returned to the original measurement input signal Vinput side, the oscillation of the signal generator 36 is stopped, and the calibration operation is completed. After that, the measurement signal Vinput
By reading out the logarithmic correction table 79 and performing correction, logarithmic conversion can be performed by correction with stable accuracy in the current circuit state and temperature state. By the way, in the logarithmic conversion calculation, in the output data Dad from the AD converter 76, the calibration value obtained above, for example, 1.5 dB.
The means for correcting the measured value between the steps reads the logarithmic correction table 79 before and after, and obtains it by calculation by the linear interpolation method. This is the same correction means as the conventional one.

In the above description of the first and second embodiments, the BPF 72 is provided in the middle of the six-stage limiting amplifiers 21 to 26 to reduce the noise signal, but the configuration may be eliminated if desired. Further, in the above description of the first and second embodiments, the case of the six-stage limiting amplifiers 21 to 26 has been described.
If necessary, the limiting amplification unit 20 may have n stages.

[0022]

Since the present invention is configured as described above, it has the following effects. The gain of the first-stage limiting amplifier 21 is set to 16 dB or 26 d.
By increasing the value as shown in B, the effect of improving the NF characteristic by about 4 to 8 dB can be obtained. As a result, the effect of improving the dynamic range of the logarithmic amplifier circuit can be obtained. In addition, by reducing the number of stages of the limiting amplifier, it is possible to obtain an effect that the circuit scale is reduced and the cost is reduced. In the second embodiment, the calibrating unit 30 is provided to calibrate at any time to prevent changes in the individual limiting amplifiers 21 to 26 of the limiting amplifying unit 20 with time, and increase in logarithmic conversion error due to temperature changes. In addition, the series connection of the limiting amplifiers 21 to 26 has an effect that the accumulated error can be eliminated and the logarithmic conversion can always be performed with stable measurement accuracy.

[0023]

[Brief description of drawings]

FIG. 1 is a logarithmic amplification block diagram of the present invention in which the gain per stage of a logarithmic amplifier circuit is increased and the number of stages of a limiting amplifier is reduced.

FIG. 2 is a block diagram of logarithmic amplification when the gain of the first-stage limiting amplifier 21 is made variable and calibration means for calibrating the linearity of logarithmic conversion is provided according to the present invention.

FIG. 3A is a logarithmic amplification block diagram of a conventional 10-stage limiting amplifier. (B) It is an internal circuit block diagram of a limiting amplifier.

FIG. 4 is a diagram for explaining a logarithmic conversion characteristic curve by a plurality of stages of limiting amplifiers.

[Explanation of symbols]

 20 Limiting amplification section 21, 22-26 Limiting amplifier 28 Gain switching section 30 Calibration section 32 MUX (switching) 34 Variable attenuator 36 Signal generator 38 Control section 42 Temperature sensor 51-60 Limiting amplifier 72 BPF 74 Detection section 76 AD Converter 78 Logarithmic scale correction unit 79 Logarithmic correction table 81 Amplifier 82 Limit voltage 83 Adder

Claims (3)

[Claims] 1. A limiting amplification section (2) which receives an input signal (Vinput) and is constituted by a plurality of stages of limiting amplifiers connected in series.
The signal logarithmically converted by (0) is detected by the detection unit (74), quantized by the AD converter (76) and converted into a digital signal (Dad), and then the logarithmic correction table (78) is calculated by the logarithmic scale correction unit (78). 79) In a logarithmic conversion circuit that performs correction calculation with the correction value from and outputs a logarithmic conversion signal, the gain setting of the first stage of the limiting amplifier exceeds 16 dB, and
A logarithmic amplifier circuit comprising a limiting amplifier (21) having a gain setting of less than dB and including the above. 2. A limiting amplification section (2) which receives an input signal (Vinput) and is constituted by a plurality of stages of limiting amplifiers connected in series.
The signal logarithmically converted in 0) is detected by the detection unit (74),
After this signal is quantized by an AD converter (76) and converted into a digital signal (Dad), a logarithmic conversion is performed by a logarithmic scale correction unit (78) for correction calculation with a correction value from a logarithmic correction table (79) and output. In the circuit, a gain switching unit (28) for switching the gain setting of the limiting amplifier (21) at the first stage is provided, and a logarithmic correction table (79) corresponding to the switching of the gain setting of the limiting amplifier (21) is provided. A logarithmic amplifier circuit characterized by doing. 3. A limiting amplification section (2) which receives an input signal (Vinput) and is constituted by a plurality of stages of limiting amplifiers connected in series.
The signal logarithmically converted by (0) is detected by the detection unit (74), quantized by the AD converter (76) and converted into a digital signal (Dad), and then the logarithmic correction table (78) is calculated by the logarithmic scale correction unit (78). 79) in a logarithmic conversion circuit that performs a correction calculation with the correction value from and outputs a logarithmic conversion signal.
4) The calibration signal from 4) is switched to the limiting amplifier (20).
And a signal generator (3) for outputting a known signal level for calibration.
6) is provided, and a variable attenuator (34) that receives the signal from the signal generator (36), attenuates it to an arbitrary amount of attenuation, and supplies it to one side of the switch (32) is provided, In response, the signal generator (36), the variable attenuator (34) and the switch (32) are controlled,
A known signal level is supplied to the limiting amplification unit (20) for measurement, a logarithmic correction value is calculated, stored in a logarithmic correction table (79), and a control unit (3 for controlling the series of calibration operations is performed.
8) is provided and the above is provided, The logarithmic amplifier circuit characterized by the above-mentioned.