JPS5912803Y2 - Detection device with temperature compensation - Google Patents

Description

[Detailed description of the invention] The present invention relates to temperature compensation in a linear detection circuit that uses a diode to output a signal of a certain polarity, and in which a positive or negative bias voltage is applied to the end of the diode output via a resistor. .

Usually, a circuit as shown in FIG. 1 is used for linear detection.

In the figure, 1 is a coil, 2 is a diode, 3 is a low frequency amplifier, 4 is an output resistor, and 5 is a bias resistor.

Resistor 5 is connected to a negative voltage source, which causes diode 2
It is well known that a bias current is passed so that detection is performed in the straight line portion of .

Incidentally, signals such as video signals that include a DC component as a frequency component are often required to transmit not only the AC component but also the DC component.

For example, a signal delay circuit using an ultrasonic delay line (v') includes a modulation/demodulation circuit, but the delayed demodulated signal must include both alternating current and direct current changes.

Here, if we focus on the demodulation stage 1', unless post-processing such as DC regeneration is performed in the subsequent stage, the demodulation stage and subsequent stages must be coupled in a DC manner.

The problem here is the variation due to the temperature of the diode.

- For example, in Figure 1, diode 2 is a germanium diode, output resistor is 5.6CKΩ],
The bias resistor is 133CKΩ], the negative bias voltage Vcc is -15[V], and the detected wave signal level is 400[V].
FIG. 2 shows the temperature fluctuation of the demodulated output when [mVp-p] is constant.

As is clear from Figure 2, this circuit has a fluctuation of more than 7Qmv within the temperature range of 0 to 50°C, and the
, the DC level will fluctuate.

When the level of the demodulated signal is high, for example, when it is higher than I Vpp, the relative error is small and can be ignored, but as the demodulated signal level becomes smaller, the harmonic error becomes larger, and the fluctuation of the DC level becomes It becomes something that cannot be ignored.

The purpose of the present invention is to compensate for DC fluctuations in the detected output due to temperature changes in a diode linear detection circuit, and to reduce errors in low-level output.

An example is shown in FIG. In the figure, 6 is a matching coil, 7 and 8 are diodes with the same characteristics, 9 is a low frequency transducer, 10 is a filter termination resistor, 11 is a resistor with the same resistance value as 10, and 12 and 13 are for bias. The resistance value of the resistor 13 is about % of that of 12, and the diodes 14 and 15 have the same characteristics as 7 and 8, and are thermally coupled to 7 and 8.

16 is a high input impedance DC amplifier, 17 and 18 are terminals each connected to a positive voltage source and a negative voltage source, and their values are +V,
-V.

Next, the operation of FIG. 3 will be explained together with FIGS. 4 and 5.

FIG. 4 is a DC equivalent circuit of the circuit in FIG. 3, and the correspondence with FIG.
10 becomes 20, 11 becomes 22, 12 becomes 23, 13 becomes 2
4, 17 corresponds to 25, and 18 corresponds to 26.

Now, if the absolute value v1 of the voltage at the terminals 25 and 26 is sufficiently larger than the temperature fluctuation range △■8□ at the terminal 27, then IB□.

IB□ can always be considered constant, and IB□=2
Resistor 23 RB□ and resistor 24RB so that it becomes 1B□
If you choose the value of □, ID1+IRL=ID1'+IRL =IB□=IBV
2=constant...(1).

Under this condition, the forward voltages of diodes 19 and 21 are equal, so if this is set to 1, the potential of terminal 27 is V
B, =O-VF...(2) Terminal 28 No N position C VB
I + VF = 0-(3) Now, if the temperature rises from TloC to T2°C in this circuit, the forward voltage shown on the horizontal axis of the graph will change from point 30 to point 30 as shown in Figure 5. 29 decreases by Δ■F, so the potential of terminal 27 is ■8□=O-(V, -△VF)...
(4) Potential of terminal 28 vB□-VB□+(VF-△■
F)-〇...(5) It can be seen that the DC potential ■B2 does not change with respect to temperature.

Also, as shown in Figure 3, the demodulated signal is sent to the amplifier via the resistor 11, and the value of 11 is generally 1 to 5 Ω, whereas the value of 12 is a resistance of several hundred KΩ or more, so it is attenuated. is small.

As an actual example, in the circuit of FIG. 3, 7. 8.14
．． 15 is a germanium diode for detection, 10.11 is 1.8 Ω, 12 is 133 Ω, 13 is 68 Ω resistor, ±■ is ±15 V, and the detected wave signal is 25 MH.
The temperature fluctuation of the demodulated signal level at 2400 mvp-p is less than 10 mV in the range of 0 to 50°C, which is an improvement of more than h compared to the conventional example shown in FIG.

In the above embodiment, the case of positive polarity signal output has been described, but it goes without saying that in the case of negative polarity, the diode polarity and the bias power supply can be simply replaced with the negative one.

As described above, according to the present invention, it is possible to obtain a demodulated output with less DC level fluctuation due to temperature in a DC-coupled diode detection circuit.

[Brief explanation of the drawing]

Fig. 1 is a basic circuit diagram of a conventional detection circuit, Fig. 2 is a graph showing the temperature fluctuation of the output in the conventional example, Fig. 3 is a temperature compensated detection circuit diagram of an embodiment of the present invention, and Fig. 4 This figure is a DC equivalent circuit diagram of FIG. 3, and FIG. 5 is a characteristic diagram of the diode used in the embodiment of FIG. 3. 7, 8.14.15...Diode, 9...Low pass filter, 10, 11.12.13...Resistor, 16...
・DC amplifier.

Claims (1)

[Scope of utility model registration request] A detection diode whose input terminal is grounded via a transformer coil, a low-pass filter connected to the output terminal below the detection diode, a terminating resistor of this low-pass filter, and a detection diode connected to the output terminal below the detection diode. In a detection device having at least a first bias resistor connected between the output terminal of the diode and the terminal to the first power supply, the terminal resistor is substantially the same as the terminating resistor. One end of a parallel connection circuit formed by connecting in parallel a resistor having a resistance value of ' and another diode having the same characteristics as the detection diode is connected to the termination resistor, and a The polarity of the electrode on the terminal resistor side of the diode is made to be the same as the polarity of the electrode on the output end side of the detection diode, and the other end of the parallel connection circuit is
The voltage values of the first power source and the second power source are connected to one end of a second bias resistor connected to a terminal of a second power source having a polarity opposite to that of the first power source and having substantially the same absolute value of voltage. The current flowing through the bias resistor and the second bias resistor is set to be sufficiently large compared to the detection output voltage value so that the current flowing through the bias resistor and the second bias resistor becomes constant, and the ratio of the DC current flowing through the first bias resistor and the second bias resistor is 2:1. A temperature-compensated detection device characterized in that the resistance values of the first and second bias resistors are selected such that the detection output is extracted from a connection point between the second bias resistance and the connection circuit.