JPS617984A - Logarithmic converting circuit - Google Patents

Abstract

PURPOSE:To convert continuously a logarithmic conversion characteristic by constituting a titled circuit so that each current value of a coupled emitter is variable, and also the sum total of each current value is constant, and making a current value supplied to each emitter variable continuously. CONSTITUTION:The current value of a constant-current source being a supply current to common number-logatithm converting parts DA1, DA2 is diverted so that in the limit, when a supply value to one converting part is set to ''0'', a supply current to the other logarithmic converting part goes to 210. In such a case, a diversion ratio is set as alpha, alpha210 and (1-alpha)210 are diverted to the converting part DA1 and the converting part DA2, respectively, and the circuit is constituted so that the sum total of each current value goes to constant. That is to say, the respective collectors of a current diverting circuit DA3 are connected to the emitters of the converting parts DA1, DA2, and the supply current is made variable by varying a control voltage Vc being the other input to a threshold voltage Vk. According to such a constitution, a logarithmic conversion characteristic can be changed continuously.

Description

DETAILED DESCRIPTION OF THE INVENTION fa) Industrial Application Field The present invention relates to a logarithmic conversion circuit whose input/output characteristics can be continuously changed.

In an ultrasonic diagnostic apparatus, the level of the received ultrasonic waves varies greatly depending on the properties of the reflecting body (for example, the tissue of the subject), so the reflected signal processing section needs to have a range of about 60 dB.

In order to display this ultrasonic signal on a cathode ray tube, which has a range of only about 20 dB, some kind of range compression means is required, and a logarithmic conversion circuit is often used for this purpose. many.

When the above-mentioned logarithmic conversion circuit is used in an actual ultrasound diagnostic device, the characteristics of the compression means are always changed depending on the living tissue to obtain the best ultrasound image. There is a problem that the compression characteristics of the circuit cannot be changed continuously, and a logarithmic conversion circuit that can change the compression characteristics continuously has been required.

tb) Prior Art As a conventional logarithmic conversion circuit, for example, the integrated circuit TL441 manufactured by Texas Instruments (TI) is well known, and an example thereof is shown in FIG.

In FIG. 2, (a) shows the configuration of the logarithmic conversion circuit, and (b) shows the compression conversion characteristics of the logarithmic conversion circuit.

In this figure (A), when the switches SL and 52 are off, each of the common number-to-logarithm conversion units DAI and DA2
Since the two inputs are balanced, transistor Ql,
IO/2 flows through the collector of Q2, and collector resistance R1
, R2 has an output Eo-+V corresponding to the collector current.
-IO·R1 is obtained at the output terminal Eo.

Next, consider when the input Ei is at an extremely low level.
Regardless of whether the switches Sl and S2 are on or off, IO/2 flows through the respective collectors of the common logarithm converters DAI and DA2, and the collector resistors R1 and R2
IO is flowing in each.

Here, when the switch S1 is turned on and the level of the input Ei increases, the collector current 1i of the transistor Q1 of the DA1 section increases linearly in proportion to the logarithm of the input Ei. , Eo= +V-(Ii+IO) ・The output voltage of R1 is obtained, and the logarithmic conversion output for the input voltage Ei (i.e., I
f-R1) will be obtained.

Then, when Ei becomes extremely large, transistor 1
If it is saturated, a constant current 10 flows and D
Since a current of 10/2 is also flowing through the old transistor in A2 section, 10+IO/2=31 is flowing through the collector resistor R1.
A constant value of 0/2 will flow.

The logarithmic conversion characteristic at this time is shown in (3) in Figure (b).

Next, when the switch S1 is off and the switch s2 is on, a 15 dB
Since the linear amplifier L^ is connected, Ei is 15
At a dB lower level, the conditions are the same as those of the common number-to-logarithm conversion unit DAI, and the operation is the same as described above, so that it exhibits the logarithmic conversion characteristic of (2) in Figure (B).

And switch 51. It can be seen that when both S2 are on, the logarithmic transformation characteristics of (2) and (3) above are combined, and the logarithmic transformation characteristic shown in (1) is exhibited.

To summarize the logarithmic conversion characteristics of the above conventional method, in (1), when switches Sl and S2 are on, the output is 30 dB.
Logarithmically transforms the input Ei in the range of , (2) logarithmically transforms the input Ei in the range of 15 dB when only switch S2 is on, and (3) logarithmically transforms the input Ei in the range of 15 dB when only switch S1 is on. Logarithmically transform Ei.

However, the input level at which the logarithmic conversion characteristic becomes linear is 15 dB higher than in case (2).

(Problem to be solved by the C1 invention) In the conventional method, as shown in Figure 2 (b), (1) * (2) or (1) g (3) However, there was a problem in that the logarithmic transformation characteristics could only be changed discretely.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional drawbacks, it is an object of the present invention to provide a method that can continuously change logarithmic conversion characteristics.

+dl Means for solving the problem and the purpose thereof is to provide a logarithmic conversion circuit having a plurality of emitter-coupled common number-to-logarithm conversion units, in which each current value of the coupled emitters is variable, and each current value is variable. This is achieved by the logarithmic conversion circuit of the present invention, which can continuously change the logarithmic conversion characteristics by configuring the sum of the values to be substantially constant and by making the current value supplied to each of the emitters continuously variable. Further, by changing the current value supplied to the emitter according to the output signal of the logarithmic conversion circuit, more preferable ultrasonic inverse i4 signal processing can be performed.

+8) In other words, according to the present invention, in the conventional logarithmic conversion circuit, the plurality of common-logarithmic conversion sections are configured with differential amplifiers having constant current sources, so that the logarithmic conversion characteristics can only be changed discretely. Focusing on the fact that it cannot be changed, we decided to make the current source of each common number-to-logarithm converter a variable current source, but supply it from the collector side of each current shunt circuit composed of a differential amplifier. , the threshold voltage Vk that is one input of the differential amplifier
Since this is made variable by changing the control voltage νC which is the other input to the control voltage Vc, there is an effect that the logarithmic conversion characteristic can be continuously changed simply by changing the control voltage Vc.

Furthermore, by shifting the above Vc to the output signal of the logarithmic conversion circuit, there is an effect that the ring-down time of the output signal with respect to the input signal of the logarithm conversion circuit can be shortened. An example will be explained in detail with reference to the drawings.

Figure 1 (Figure 1 shows an embodiment of the present invention, (B)
shows an example of its logarithmic transformation characteristics.

As is clear from this figure, the main focus of the present invention is on the two common number one-logarithm conversion units D^1. The supply current to DA2 is divided by the current value of the constant current source (however, the current value is 2IO), and in the limit, when the supply 4n to one logarithmic conversion section is set to "0", the supply current to the other logarithmic conversion section is 210, but in general, if the dividing ratio is α,
For example, the common number-to-logarithm conversion unit DAI is configured to branch to α210, and the common number-to-logarithm conversion unit DA2 is configured to branch to (1-α)210.

In FIG. 1, DAI and DA2 are the emitter-coupled common-logarithm converters described in FIG. 2, and their emitters are connected to respective collectors of a current shunt circuit DA3.

and vk: dark value voltage vc two control voltage are shown respectively.

Here, if we consider the case when Vc = Vk, the two inputs of the current shunt circuit DA3 are balanced, so
The respective collector currents are 10, and they operate so as to supply the same emitter current IO to the common number-to-log conversion units DAI and OA2, so that the common number-to-log conversion units 081. DA2 operates to function as a logarithmic conversion circuit corresponding to case (1) in FIG. If this is the case,
This corresponds to the case where the split flow ratio α-0.5.

From this state, when the control voltage Vc increases in the direction of Vc > Vk, the collector current α210 of the transistor 03 becomes the collector current (1-
α) Becomes larger than 2IO.

Conversely, when the control voltage Vc increases in the direction of Vc<Vk, the collector current α210 of the transistor Q4 becomes smaller than the collector current (1) of the transistor Q4.
-α) Operates to be smaller than 2IO.

When the control voltage Vc reaches its maximum value in the direction of Vc > Vk, the current supplied to the emitter of the common logarithmic converter DAI reaches the maximum value of 2IO, and the supply current to the emitter of the common logarithmic converter DA2 increases. teeth.

0, and the operation corresponds to (3) in FIG.

That is, when the input Ei is at a low level, the transistors 011 and 2 of the common number-to-log conversion unit 081 each
When a collector current of 0 flows and Ei increases, the input E
The collector current of the transistor increases linearly with respect to the logarithm of i.

In practice, due to the voltage-current characteristics of transistor Q1,
The above logarithmic transformation is not performed unless the input Ei increases to a certain level. Then, when the transistor 01 becomes saturated, the collector current becomes 2IO and becomes constant. This state is the case α-1.

Next, when the control voltage Vc shows the maximum value in the direction of νC<ν, the current supplied to the emitter of the common number-to-logarithm conversion unit DA2 reaches the maximum value of 210, and the common number-to-logarithm conversion unit D
The current supplied to the emitter of AI becomes "0" and the operation corresponds to (2) in FIG. 2.

That is, when the input Ei is at a low level, each of the transistors 11 and 2 of the common number-to-log conversion section DA2
When a collector current of 0 flows and Ei increases, the input E
The collector current of the transistor increases linearly with respect to the logarithm of i.

Then, when the transistor 01 becomes saturated, the collector current becomes 210 and becomes constant. This state is the α-0 case.

However, in this case, the input terminal of the common number-to-logarithm conversion unit DA2 is connected to the input terminal Ei of 15
Since a dB amplified signal is input, the absolute value of the input level at which the logarithmic conversion characteristic becomes linear is lowered by 15 dB, and the conversion characteristic corresponds to (2) in FIG. 2.

The above operation is performed using the input voltage Ei on the X axis and the collector resistance R.
The graph shown in (b) shows the current I flowing through the current shunt circuit DA as the Y axis.
For the threshold voltage Vk of 3, Vc<Vk (α-0)
4Vc=Vk (α=0.5) #Vc>Vk (α=1
), it can be seen that continuous logarithmic transformation characteristics as shown in the figure can be obtained.

Here, for the control voltage Vc giving 0≦α≦1, in the common number-to-logarithm conversion unit DAI, the maximum level of the input voltage Ei at which the logarithmic conversion characteristic becomes linear is +15 dB, the minimum level is OdB, and the common number is In the logarithmic conversion section D^2, if the minimum level of the input voltage Ei at which the logarithmic conversion characteristic becomes linear is -15 dB, and the maximum level is OdB, then when α-00, the logarithm is converted between Ei = -15 dB and OdB. The conversion characteristic becomes linear, and when α-1, the logarithmic conversion characteristic becomes linear between Ei=OdB and +15 dB.

Therefore, between 0 and α and 1, by changing the control voltage Vc from a value smaller than the threshold voltage Vk to a value larger than the threshold voltage Vk, -15dB≦Ei≦OdB, the logarithm of the common number 1 logarithmic conversion part DA2 According to the conversion characteristics, when OdB≦Ei≦+15dB, the common number one-log conversion part D
It operates according to the logarithmic transformation characteristics of AI.

As mentioned above, if it deviates from α・0.5, 1. Although it deviates from perfect logarithmic characteristics, it does not pose much of a problem in ultrasonic diagnostic equipment and the like.

Next, an example in which the logarithmic conversion circuit of the present invention is applied to, for example, an ultrasonic diagnostic apparatus with a signal of 1 fM and a short duration will be described with reference to FIG.

Conventionally, the use of a logarithmic conversion circuit has been particularly widely used in the above-mentioned ultrasonic diagnostic apparatus because it is possible to pick up and display signals having a wide range without omission.

However, the waveform of the signal received by the ultrasonic transducer tends to have tails due to multiple reflections of the ultrasonic signal within the vibration layer within the ultrasonic transducer, and the logarithmic conversion circuit emphasizes the tails. In many cases, the image quality deteriorated.

Therefore, as in the example shown in FIG. 3(A), by configuring the output signal of the logarithmic conversion circuit to be the control signal Vc explained in FIG. It is possible to obtain an output signal Eo with short down time,
The image quality of ultrasonic tomographic images in an ultrasonic diagnostic apparatus can be improved.

In FIG. 3(a), 1 is the logarithmic conversion circuit of the present invention explained in FIG. 1, Ei+Vc is the same as that explained in FIG. 1, and Vc is the output signal of the logarithmic conversion circuit 1. E
It is distinctive in that it is o.

When the logarithmic conversion circuit 1 of the present invention is applied in this way, the control voltage Vc and the waveform of the output signal EO of the logarithmic conversion circuit 1 are determined by (Ro) ) will be explained below.

(b) In the figure, ■ indicates the waveform of IEi, and
The logarithmic conversion characteristics of the logarithmic conversion circuit 1 explained in the figure are shown below. However, in the case of Vc > Vk), ■ is Vc.

The waveform of Eo is shown.

For example, in ■, the input voltage at time L3 is Ei3
Then, the control voltage Vc at the same time t3 from ■ is V
c3, so in the graph ■ of logarithmic transformation characteristics,
It shows the conversion characteristics indicated by the parameters (t3, t5).

Therefore, the logarithmic conversion circuit l for the ultrasonic reception signal Ei3
The output signal EO of will take the value indicated by EO3 in the waveform of Eo in the graph of (2).

Following the same procedure, for example, if we calculate the waveform of Eo with respect to Ei from time tO to t7, we can find the waveform of Eo at each time.
Since the logarithmic transformation characteristics are determined according to
It can be seen that an output waveform EO with a short ring-down time can be obtained with respect to the human input signal Ei (indicated by a dotted line in the figure).

fg) Effects of the Invention As explained in detail above, the logarithmic conversion circuit of the present invention has a plurality of emitter-coupled common number-to-logarithm conversion sections, and the logarithmic conversion circuit has a plurality of emitter-coupled common number-to-logarithm conversion sections. is variable and the sum of each current value is approximately constant, the collector side of the current shunting circuit composed of a differential amplifier is connected to the emitter of the logarithmic conversion circuit, and the differential Since this is made variable by changing the control voltage Vc, which is the human power of the other input, with respect to the dark value voltage Vk, which is one input of the amplifier, the logarithmic conversion characteristic can be made continuous by simply changing the control voltage Vc. There are effects that can be changed.

Furthermore, when the means for configuring the output signal of the logarithmic conversion circuit to be the control signal Vc explained in FIG. 1 is applied to an ultrasound diagnostic apparatus, for example,
An output signal Eo with a short ring-down time can be obtained, and the image quality of ultrasound tomographic images in an ultrasound diagnostic apparatus can be improved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention and its logarithmic conversion characteristics. FIG. 2 is a diagram showing a conventional logarithmic conversion circuit and its logarithmic conversion characteristics. FIG. 3 is a diagram illustrating the effect of shortening the ring-down time of an ultrasonic reception signal by applying the logarithmic conversion circuit of the present invention to an ultrasonic diagnostic apparatus. In the drawing, DAI and DA2 are common number-to-logarithm conversion units. DA3 is a current shunt circuit, and LA is a 15dB linear amplifier. Ql, mouth 2. and Q3. Q4 is a transistor. SL and S2 are switches. R1 and R2 are collector resistors, and Ei is an input signal. EO is the output signal, and 10 is the current value of the constant current source. ν is the dark value voltage, and Vc is the control voltage. α is the diversion ratio. are shown respectively.

Claims (2)

[Claims] (1) A logarithmic conversion circuit having a plurality of emitter-coupled common number-logarithm conversion sections, in which the current value of each current source connected to the combined emitter terminal is variable, and the current value of each current source is variable. A logarithmic conversion circuit characterized in that it is configured such that the sum of the sum is approximately constant. (2) The logarithmic conversion circuit according to claim 1, wherein the current value of each of the current sources is controlled by an output signal of the logarithmic conversion circuit.