JP3468197B2 - Method for measuring gain of variable amplifier - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a variable gain variable amplifying device used for taking in an analog signal for servo control and a method of measuring the gain thereof. In recent years, with high integration and high accuracy of LSIs, high-precision devices are also required for LSI evaluation and characteristic measurement, and costs and time burdens are increasing. Hereinafter, a conventional variable amplifying device will be described with reference to the drawings. FIG. 2 is a circuit diagram of a conventional variable amplifying device. Hereinafter, each block will be described. [0004] Reference numeral 1 denotes an input terminal to which an amplified signal is input;
Is a reference voltage terminal to which a reference voltage is applied. Reference numeral 3 denotes a variable attenuator which has a variable magnification and adjusts the gain of the signal to be amplified. The variable attenuator 3 includes a ladder resistor 4, an insertion resistor group 5, and a switch group 6. Reference numeral 4 denotes a ladder resistor, which is connected to the input terminal 1 and the reference voltage terminal 2 at both ends and has a plurality of output terminals at different positions. In this example, five resistors R1 to R
Consists of five. Reference numeral 5 denotes an insertion resistor group, which is connected to the plurality of output terminals T1 to T5 of the ladder resistor 6 so as to be in series with the five switches S1 to S5 of the switch group 6, respectively. When any one of the plurality of output terminals T1 to T5 of the ladder resistor 4 is selected (turned on) by the switches S1 to S5, the resistance value is set so that the output resistance of the variable attenuator 3 becomes a constant value. Is done. In this example, five resistors r1
To r5. Reference numeral 6 denotes a switch group, which is connected to each of the plurality of output terminals T1 to T5 of the ladder resistor 4 to select and fix a gain-adjusted amplified signal output from a predetermined location when the gain is switched. It is supplied to the gain amplifier 7. In this example, it is composed of five switches S1 to S5. Reference numeral 7 denotes a fixed gain amplifier, and the variable attenuator 3
And an operational amplifier connected in series. [0010] The gain measurement of the conventional variable amplifying device configured as described above will be described below. The amplified signal input to the input terminal 1 is input to the ladder resistor 4, and the switch group 6
Are output at a magnification according to the on / off selection state of the switches S1 to S5. An output signal from the switch group 6 is input to a fixed gain amplifier 7, and an amplified signal is obtained from an output terminal 8. Therefore, by sequentially selecting the switches S1 to S5 for turning on the switch group 6, each output level can be obtained from the output terminal 8, and each gain can be measured from the ratio of the input voltage to the output voltage. [0011] Generally, when measuring the gain of a high attenuation rate, if the input voltage has an upper limit, the difference between the voltage of the reference terminal and the voltage of the output terminal becomes small, and Accuracy measurement is required, and gain measurement is difficult. [0012] From such a background, the above-described conventional configuration has the following problems. This problem,
This will be described with reference to FIG. In the variable attenuator 3 shown in FIG. 2, the switch S4 of the switch group 6 is turned on, and the switch S
When each of 1 to S3 and S5 is turned off, the input terminal 1
, The gain of the variable attenuator 3 is the ratio of the ladder resistor 4 and It is expressed as follows. In the above equation, the difference between the voltage of the reference voltage terminal 1 and the output voltage of the variable attenuator 3 is very small due to the relationship of the numerator << denominator, and the gain measurement requires high accuracy. The present invention has been made to solve the above-mentioned conventional problems, and is provided with a new input terminal in a conventional variable amplifying apparatus, and measures the gain of a high-attenuation variable attenuator by dividing it into low-attenuation parts. Accordingly, it is an object of the present invention to enable stable and highly accurate gain measurement of a variable amplifier. According to a first aspect of the present invention, there is provided a method for measuring a gain of a variable amplifying apparatus, comprising the steps of: A gain adjustment ladder resistor having a plurality of output terminals at different positions connected to both ends of the terminal and a second input terminal for inputting a reference voltage; and one of the plurality of output terminals of the ladder resistor. A third input terminal connected to the ladder resistor and a plurality of output terminals of the ladder resistor. A plurality of switches for supplying to the amplifier, wherein the gain measuring method of the variable amplifying device is characterized in that, among the plurality of switches, a switch to which the third input terminal is connected is turned on. A first step of obtaining a first gain of the variable amplifying device as viewed from the first input terminal, and setting a certain one of the plurality of switches to a conductive state, and A second step of obtaining a second gain of the variable amplifying device as viewed, and a third step of adding the first and second gains to obtain a gain of the variable amplifying device as viewed from the first input terminal. And the following steps. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a circuit configuration of a variable amplifying device according to an embodiment of the present invention. In FIG.
Reference numerals 1 to 8 correspond to those having the same reference numerals described in the related art. The difference is that a measurement input terminal 9 provided at an arbitrary position of the ladder resistor 6 is provided. In this example, a measurement input terminal 9 is provided at the portion of T2. The measurement of the gain of the variable amplifying device according to the present invention configured as described above will be described below. The signal input to input terminal 1 is input to ladder resistor 4,
With reference to the voltage applied to the reference voltage terminal 2, a signal is output through one of the resistors r <b> 1 to r <b> 5 of the insertion resistor group 5 at a magnification according to the on / off selection state of the switches S <b> 1 to S <b> 5 in the switch group 6. . This signal is input to the fixed gain amplifier 7, and an amplified signal is obtained. This switch group 6
Is input to the fixed gain amplifier 7, and an amplified signal is obtained from the output terminal 8. Therefore, by sequentially selecting the switches S1 to S5 to be turned on in the switch group 6, each output level can be obtained from the output terminal 8, and each gain can be measured from the ratio of the input voltage to the output voltage. This is the same when the input terminal 1 is used as the measurement input terminal 9. Here, the operation resulting from the addition of the measurement input terminal 9 will be described with reference to FIG. In the variable attenuator 3 shown in FIG.
4 is turned on, and the switches S1 to S3 and S5 are turned off. (First Step) The switch S2 of the switch group 6 is turned on, the switches S1 and S3 to S5 are turned off, and the gain of the variable attenuator 3 as viewed from the input terminal 1 is obtained as follows. [Equation 2] (Second Step) The switch S4 of the switch group 6 is turned on and the switches S1 to S3 and S5 are turned off, and the gain of the variable attenuator 3 as viewed from the measurement input terminal 9 is obtained as follows. [Equation 3] (Third Step) The gain of the variable attenuator 3 in which the switch S4 of the switch group 6 is turned on and the switches S1 to S3 and S5 are turned off is calculated by the sum of (Equation 2) and (Equation 3). This is given by: The result is the same as Here, according to the gain measurement of the variable amplifying device according to the present embodiment, (Equation 2) and (Equation 3) show that the numerator <
From the relationship of the denominator, the difference between the voltage at the reference voltage terminal 1 and the output voltage of the variable attenuator 3 is not as small as in the conventional case (Equation 1). Here, the gain measuring method using the conventional variable amplifying device and the gain measuring method using the variable amplifying device of the present application will be compared using specific numerical values. Consider a case in which a gain is obtained when the switch S5 is turned on. Here, the value of each component is determined as follows. 1. 1. Voltage applied to input terminal 1: 3V 2. Voltage applied to input terminal 2: 1.5V 3. Voltage applied from input terminal 9 for measurement: 3V Resistance value (r1, r2, r3, r4, r5) = (10, 4, 2, 1,
0.5) kΩ (gain by the conventional variable amplifying device) The output voltage V0 is obtained by the following equation. [Formula 4] Therefore, the gain Gpri is obtained by the following equation. [Formula 5] (Gain by Variable Amplifying Device of the Present Invention) (1) Input 3V from the first step input terminal 1, turn on S2, and measure output voltage V0a. [Formula 6] The gain Ga at that time is obtained by the following equation. [Formula 7] (2) Second Step 3V is input from the measurement input terminal 9 and S5 is turned on to measure the output voltage V0b. [Equation 8] The gain Gb at that time is obtained by the following equation. [Equation 9] (3) The third step gain Ga and the gain Gb are added to obtain a gain Gtotal. Gtotal = -23.5db-7.4dB = -30.9d
B As described above, by providing a measuring input terminal as needed for the ladder resistance of the variable attenuator, and by separately measuring the gain of the variable attenuator having a high attenuation rate to a portion having a low attenuation rate, stable and high accuracy can be obtained. This makes it possible to measure the gain of the variable amplifying device. According to the present invention, the ladder resistance of the variable attenuator is provided with an input terminal for measurement as required, so that the gain of the variable attenuator having a high attenuation rate can be reduced by a portion having a low attenuation rate. , And a stable and highly accurate gain measurement of the variable amplifying device can be realized.

[Brief description of the drawings] FIG. 1 is a circuit diagram of a variable amplifier according to the present invention. FIG. 2 is a circuit diagram of a conventional variable amplifier. [Explanation of symbols] 1 input terminal 2 Reference voltage terminal 3 Variable attenuator 4 Ladder resistance 5 Insertion resistance group 6 Switch group 7 Fixed gain amplifier 8 Output terminal 9 Measurement input terminal

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Claims (1)

(57) [Claim 1] A plurality of terminals which are connected at both ends to a first input terminal for inputting a signal to be amplified and a second input terminal for inputting a reference voltage and have different positions. A ladder resistor for gain adjustment having an output terminal, a third input terminal connected to one of the plurality of output terminals of the ladder resistor, and a plurality of output terminals of the ladder resistor connected to each other. A plurality of switches for selecting a gain-adjusted amplified signal output from a predetermined point when the gain is switched and supplying the selected signal to a fixed gain amplifier. A first step of setting a switch connected to the third input terminal among the plurality of switches to a conductive state to obtain a first gain of the variable amplifying device as viewed from the first input terminal; The plurality of Of switch, first and one in the conductive state of said variable amplifying device seen from the third input terminal 2
And a third step of adding the first and second gains to obtain the gain of the variable amplifying device as viewed from the first input terminal. Of measuring the gain of a variable amplifying device.