JPS6310604B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a double-wave rectifier circuit that detects an AM modulated signal with good inverse characteristics.

Traditionally, a double-wave rectifier circuit has been used to detect AM modulated waves because of its good detection efficiency, good distortion characteristics, and doubling of the carrier wave, making it easier to configure the filter in the latter stage. It is used.

FIG. 1 shows a double-wave rectifier circuit as a conventional example. In FIG. 1, 1 is an input terminal for a modulated signal, 2 is an output terminal for a rectified signal, 3 is a detection terminal,
4 and 5 are reference voltage terminals, 6 is a power supply terminal, 7 is a ground potential terminal, 8 and 9 are transistors of a differential amplifier configuration for forming the same and opposite phase waveforms, and 10 and 11 are the above-mentioned transistors 8 and 9, respectively. The current source transistor in the circuit, 12 and 13 are OR circuit transistors for detection, 14 is the emitter resistor of the differential amplifier, 1
5 and 16 are load resistances, 17 and 18 are emitter resistances of current source transistors, 19 is a current source of the detection circuit, 20 is a coupling capacitor for signal input,
21 is a low-pass filter for removing carriers after detection, and 40 and 41 are bias supply resistors.

Now, if the signal shown in Fig. 2 a is input to the modulation signal input terminal 1, the collector of one of the transistors 8 in the differential circuit receives a signal b whose phase is opposite to that of the input a and which is ₁ times α. At the collector of the other transistor 9 in the differential circuit, a signal c which is in phase with the input a and which is _{twice as} large as α appears. The output from the detection OR circuit obtained by these collector signals b and c, that is, the waveform at the detection terminal 3, is in the form of double-wave rectification as shown in d. In the signal spectrum of this waveform d, 2f _c appears with respect to the signal wave f _s and the carrier wave f _c . Therefore, if the characteristics of the low-pass filter 21 connected to the detection terminal 3 are determined as shown in FIG. 2e, it is possible to sufficiently separate _fs and _fc even if they are close to each other. Although AM detection can be performed in this manner, considering the dispersion of the elements that make up the circuit shown in FIG. 1, the following problem arises. Here, Fig. 2 b, c
α ₁ vin, α ₂ vin, Vo ₁ , and Vo ₂ can be expressed by the following formulas.

α ₁ Vin＝R _L1 ／R _E Vin……(1) α ₂ Vin＝R _L2 ／R _E Vin……(2) Vo ₁ ＝V _CC −[V _B −V _BE3 ／R ₁ +(L _B2 R _B2 +V _BE2 )−(
I _B1 R _B1 +V _BE1 )/R _E 〕R _L1 ………(3) Vo ₂ =V _CC −[V _B −V _BE4 /R ₂ −(I _B2 R _B2 +V _BE2 )−(
I _B1 R _B1 +V _BE1 )/R _E ]R _L2 ......(4) First, one of the factors causing the variation is the load resistances 15 and 1 of both transistors 8 and 9 in the differential amplifier configuration.
Let us consider the case where each value of 6 is R _L1 ≠ R _L2 .
When R _L1 > R _L2 , the output waveform of detection terminal 3 is as shown in Figure 3a.
There is a difference in amplitude between the same and opposite phases as shown in . At this time, the respective DC potentials Vo ₁ and Vo ₂ of the transistors 8 and 9
Although Vo ₁ ≠ Vo ₂ , it is simply set as Vo ₁ Vo ₂ to avoid complicating the detected output waveform. Even if this waveform is passed through the filter 21, the carrier wave component f _c is hardly removed, and the third
It remains as a carrier leak component as shown in Figure b. If you simply consider R _L1 −R _L2 /R _L1 ×100=5% (relative ratio of normally used carbon resistance), it is approximately 5%.
It becomes a carrier leak.

Next, even if R _L1 =R _L2 , if Vo ₁ <Vo ₂ , for example, considering R ₁ >R ₂ , the output waveform of the detection terminal 3 will be as shown in FIG. 3c. In this case too,
As in the case of R _L1 > R _L2 , when looking at the signal after passing through the filter 21, for small input signals, there are parts where the waveform cannot be reproduced. This results in distortion and detracts from the advantage of using a double-wave rectifier circuit. for example
When R _L1 = R _L2 = R _E = 1KΩ, I _E4 I _E3 = 1 mA, transistor h _FE = 100, and signal input Vin is 1V _pp , R ₁ − R ₂ / R ₁ × 100 = 5%. Assuming that I _E4 - I _E3 /I _E4 ×100 = 5%, an error of 50 μA occurs for 1 mA, Vo ₁ - Vo ₂ = 50 mV, and the output
For a 500mV _pp waveform, 50/2mV = 25mV appears as an error. This can also be considered to correspond to a distortion component of approximately 5%.

In this way, if the resistance value is not selected very carefully, it can be considered that distortion and carrier leakage of about 5% will occur. The present invention provides a double-wave rectifier that has significantly improved carrier leakage and distortion characteristics.

FIG. 4 shows an embodiment of the present invention, and FIG. 5 shows signal waveforms of its main parts. In Figure 4, 2
2 and 23 are PNP OR circuit transistors that perform negative polarity detection, and 24 and 25 are positive polarity detection.
NPN OR circuit transistors, 26 and 27 are level shift transistors, 28 and 29 are transistors for a differential addition circuit for positive and negative detection waveforms, 30 is an output emitter follower transistor, 31 is an emitter resistor for the differential addition circuit, 32 is the collector load resistance, 33, 34, 35, 36, 37, 38, 39
is a constant current source, and has the same configuration as in FIG. 1 except for the above.

A modulated signal similar to that shown in Figure 2a is input to input terminal 1.
When input to the level shift transistor 26, only the negative half wave is extracted at the common emitter point of the PNP OR circuit transistors 22 and 23.
After passing through, the waveform appears at the base of one transistor 28 of the differential adder circuit as shown in FIG. 5c.
On the other hand, the NPN transistors 24 and 2 of the above OR circuit
Similarly, only the positive half wave of the waveform detected by 5 is taken out to the base of the other transistor 29 of the differential adder circuit through another level shift transistor 27, as shown in FIG. 5b. There is. At this time, the output of the differential adder circuit, ie, the collector of the transistor 28, always combines the base potential difference components, as shown in FIG. 5d. Here, V _C = V _CC − [I ₃₇ + (V _B13 − V _B14 ) 1/R _E ] R _L
−V _BE15 V _B13 =V _REF −I _B2 R _B2 −V _BE8 +V _BE11 V _B14 =V _REF −I _B1 R _B1 +V _BE9 −V _BE12 I ₃₇ is the current value of the current source 37 Let's also consider dispersion in the same way.

First, when considering V _B14 >V _B13 , it can be considered as shown in Figure 6a, so the output waveform of terminal 3 will be as shown in Figure 6b. V _CO is the collector DC potential of the transistor 28 when V _B13 = V _B14 in a no-signal state. Similarly, in the state of V _B14 <V _B13 , the waveform shown in FIG. 6c is considered to be obtained, so that the output of the detection terminal 3 has the waveform shown in FIG. 6d. Figure 6b above,
As is clear from each waveform of d, carrier leakage,
No distortion or the like occurred. In addition, the paths to the bases of the differential adder transistors 28 and 29 can be simply regarded as emitter followers, so there is little attenuation of the signal amplitude, and furthermore, the transistors 24 and 26 are NPN, and the transistors 22 and 27 are PNP, so both signals are connected to each other. Since the obtained circuit configuration has a complementary connection, there is almost no variation in the amount of attenuation, and the phenomenon shown in FIG. 3a does not occur. V _C1 at output terminal 3,
A deviation from V _CO such as V _C2 becomes a problem only as a variation in the output dynamic range, and has no effect on carrier leak or distortion. Furthermore, since the transistors PNP and NPN are used complementary, the deviation between V _C1 and V _C2 is small.

In this way, by simply combining transistors that match the polarity, a substantial double-wave rectification can be configured, and the present invention can eliminate the deviation of the DC component when combining both polarities of the detection using a differential amplifier circuit. If so, it will have a great effect on reducing carrier leakage and distortion as a double-wave rectifier.

[Brief explanation of the drawing]

Figure 1 is an electrical circuit diagram of a conventional double-wave rectifier, Figures 2 and 3 are characteristic diagrams of a conventional double-wave rectifier, and Figure 4 is an electrical circuit diagram of a double-wave rectifier that is an embodiment of the present invention. The circuit diagram of FIG. 5 and FIG. 6 are diagrams each showing an example of the characteristics of the double-wave rectifier according to the present invention. 1... Input terminal, 2... Output terminal, 3... Detection terminal, 4, 5... Reference voltage terminal, 6... Power supply terminal, 7... Ground potential terminal, 21... Low pass filter, 22, 23, 24, 25, 26, 27,
28, 29...transistor, 33, 34, 3
5, 36, 37, 38, 39...constant current source.

Claims (1)

[Scope of Claims] 1. A first detection transistor pair that detects only a voltage waveform higher than a reference voltage with respect to an input signal, and only a voltage waveform whose polarity is opposite to that of the first detection transistor and is lower than the reference voltage. and a third transistor pair that converts the voltage waveforms detected by each of the detection transistor pairs into currents and synthesizes them so that they have the same polarity. A double wave rectifier. 2 The first detection transistor pair and the second detection transistor pair have opposite polarities, and the signals detected from each of the detection transistor pairs are passed through each emitter follower transistor and then transmitted to each of the third transistor pair. A double-wave rectifier according to claim 1, characterized in that the input is: