WO1983000782A1

WO1983000782A1 - Amplitude modulation circuit

Info

Publication number: WO1983000782A1
Application number: PCT/JP1982/000321
Authority: WO
Inventors: Ltd. Sanyo Electric Co.
Original assignee: Maeda, Tetsuhiro; Hosoya, Nobukazu
Priority date: 1981-08-19
Filing date: 1982-08-17
Publication date: 1983-03-03
Also published as: JPS5831601A; KR840001491U; KR860000896Y1

Abstract

An amplitude modulation circuit which has no modulation distortion even at high modulation factors while still maintaining its ability of high integration. In an amplitude modulation circuit having a first differential pair (D1) with a constant-current source (S1) and a second differential pair (D2) using one (T1) of the transistors forming the first differential pair (D1) as a common emitter current source, in which a modulation signal is input to one differential pair (D1) and a carrier is input to the other differential pair (D2), a bypass circuit (B) which passes a constant current in proportion to the current of the source(S1) is connected in parallel to the second differential pair (D2) receiving the carrier, so that the operation start point of the second differential pair (D2) is advantageously increased to the vicinity of the starting end of the low frequency band side of the linear range of the AM modulation. Such an amplitude modulation circuit can be used for an RF converter which constitutes the interface between video equipment and a television receiver.

Description

Details

Title of invention

Amplitude modulation circuit

Technical field

The present invention relates to an amplitude modulation circuit

Background art

For example, radio frequency converters (Radio Frequency Converters) that interface with video equipment such as video tape recorders and ordinary television receivers It has a built-in “AM modulator” under an amplitude modulator that amplitude-modulates RF waves (VHF or UHF) of a predetermined channel with a video signal.

Such an AM modulation circuit has recently been often incorporated into an integrated circuit (hereinafter, referred to as an “IC”). For example, the first differential pair and the differential pair are connected to each other. There has been proposed an AM modulation circuit suitable for integration into an IC having a second differential pair using one of the transistors to be formed as a common emitter current source. Specifically, as a prior art suitable for this kind of IC, a circuit shown in FIG. 1 or FIG. 2 can be given.

These AM modulation circuits basically consist of a constant current source (Si)

'' O PI Differential pair (Dl) using a pair of transistor (Tl) and (T2 :) as a common emitter current source, and one of the transistor pair (Tl) ) a pair of bets run-g is te (T3), is constructed out (second differential pair to common E Mi jitter current source of T ₄₎ (D2). The modulated input signal is input to the base of one of the transistor pairs (の 2) forming the first differential pair having the second differential pair (D2) as an unbalanced load, and Is input to the base of one of the transistors (T3 :) forming the _second differential 对 (D 2) with the resistor ( _Rl ) as an unbalanced load (and each transistor In an AM modulation circuit in which a predetermined DC bias voltage is individually applied to the other ten transistors (Tl) and (T4) of the star pair, the transistors and : ⁴ ) The maximum and minimum peak-to-peak values of the modulated wave (Fig. 3) output from the collector (Fig. 3) are A and B, respectively. ,

A B

M = X 1 0 0 C ^)

Expressed as A + B

In the circuit of Fig. 1, while the modulation factor M is small,

The difference between the differential 对 (Dl) and the constant current source (S i)

'' OMPI The dynamic amplifier operates in the linear region. Fig. 4 shows the input / output characteristics (Cl) of this differential amplifier circuit. In the characteristic diagram, the horizontal axis represents the voltage value (Vi) obtained by subtracting the modulation signal input voltage from the fixed bias applied to the base of the transistor (Tl), and the vertical axis represents the vertical axis. Indicates the collector current (I) of the transistor (Ti). (I 0) is the current flowing through the constant current source (Si). In addition, the emitter current of the transistor (Tl) is equal to the collector current, and the collector current is equal to the current flowing through the second differential pair (D2). And

If the circuit configuration shown in Fig. 1 is selected by selecting a predetermined circuit constant,

In addition, the linear region (L) of the input / output characteristics- (Cl) is uniquely determined in the range (0.310 to 0.710 :). The upper limit of the modulation rate (M) at which the A / M modulation can be performed within this linear region (L) is naturally determined from the power that is uniquely determined. Here, if the modulation rate is to be kept above the upper limit with this circuit configuration, it is necessary to use the non-linear regions (SH) and (SL) of the differential amplifier circuit to avoid modulation distortion. You won't get it. Incidentally, if the modulation center is set to 0.510 and it is attempted to achieve a modulation rate of 75, then 0.12510 ~ 0.8

A range of 75 I 0 is used. This clearly deviates from the rear area L (0.3 I 0 0.710 :).

, OMPI As a measure to improve the circuit in Fig. 1, as shown in Fig. 2, the emitters of the transistors (Ti) and (T2) forming the first differential pair (Dl) must be each feedback resistor (r), to insert the (r), and the this conceivable to substantially expand the Linear operation region of the differential amplifier circuit (characteristic of FIG. 4 (C _2)). However, if you still want to increase the modulation depth] 9, for example, M = 7 5

In such a case, it is difficult to secure a necessary linear area.

The present invention is to solve such problems of the prior art, that is, to maintain the suitability for IC conversion as in the prior art, and to set the modulation distortion even if the modulation is set to a high modulation rate. The purpose is to provide an AM modulation circuit.

Disclosure of the invention

This invention is characterized by adding a new improvement to the prior art circuit configuration. That is, a first differential pair having a constant current source and a second differential pair having one of the transistors forming the first differential pair as a common emitter current source are provided. In the AM modulation circuit configured to apply a modulation signal as one of the differential pair inputs and apply a carrier as the other differential pair input, the carrier is used as an input. In parallel with the differential pair, a constant of a ratio corresponding to the current of the constant current source is set.

OMPI WIPO It features a bypass circuit for passing current. This is J? , The starting point of the differential pair input with the carrier can be raised to near the low end of the linear region of AM modulation, thus achieving high modulation rate AM modulation in the linear region. be able to.

The AM modulation circuit according to the present invention is preferably implemented as an IC. Rather than combining discrete components, differential pairs can be easily equalized.The characteristics of the transistor can be equalized, and the force ^ can be configured to be very high. .

Preferably, the bypass circuit has a constant current source. The linear characteristics can be stabilized as compared with flowing a constant current in correlation with other circuit parts.

Further, in the AM modulation circuit formed as an IC, it is preferable to connect a resistor in series to the constant current source of the bypass circuit, and the carrier is connected via a collector layer of the _c- transistor. A can be effectively prevented from leaking.

In this way, an A / M modulation circuit with low modulation distortion even at a high modulation rate can be realized while maintaining the suitability for IC conversion as it is.o

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows AM modulation as a prior art suitable for IC implementation.

, OMPI It is a circuit diagram of a circuit.

Fig. 2 is a circuit diagram of another AM modulation circuit as a prior art suitable for IC implementation. '

FIG. 3 is a diagram for explaining an amplitude modulation rate.

Fig. 4 is a characteristic diagram of the AM modulation circuit shown in Fig. 2.

FIG. 5 is a circuit diagram of an embodiment of an AM modulation circuit according to the present invention.

FIG. 6 is an operation characteristic diagram showing the characteristics of the circuit of FIG. 5. FIG. _0- FIG. 7 is a circuit diagram of an embodiment of the AM modulation circuit according to the present invention, which is specifically implemented as an IC.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 5 shows an embodiment of the AM modulation circuit of the present invention, and the same reference numerals are given to the same components as those in the prior art in FIG. 1 or FIG.

AM modulation circuit of the present invention also basically Chi I ¾ including the first differential pair and (Dl) a second differential pair (D _2), the first differential pair and (Dl) The collector of the NPN transistor (T2) to be formed is connected to the common power supply line (+ Vc C), and the emitter forms the first differential pair (Di). Do

OMPI

''-WIPO It is connected to another NPN-type transistor (Ti) emitter. The commonly connected emitter is grounded via a constant current source (S i) through which a constant current (10) flows. The collector of the transistor (Ti :) forming the first differential pair (Dl) includes two NPN-type transistors forming the second differential pair (D2). (T3), ¾ a common E Mi jitter that is connected is connected to, this door run-g is te (Ti) is E Mi jitter current source of the second differential pair (D ₂₎ of (T4) You. The collector of the transistor (T 3) forming the second differential pair (D 2) is connected to the power supply line (+ Vcc), while the other transistor is connected to the power supply line (+ Vcc). The collector of the star (T4) is connected to the power supply line (+ Vcc) via the load resistor (R1).

Then, in parallel with the second differential pair (D2), a bypass circuit (B :) for flowing a constant current [11], which is the most particular feature of the present invention, is connected. In this example, the bypass circuit (B) is a series connection of a constant current source (52) and a resistor (2). Most of all, the resistor (R2) is an essential component, and is provided from the viewpoint of IC fabrication. Door run-g is te (T3), (T _4), so to scan I Tsu Chi in g at high frequency, door run-g is te of Collector power layer Canon re-A and through the capacity of Li Work

] 9, to prevent this effectively

ΟΜΡΙ

/ 0 _ The constant current (II) flowing through the bypass circuit (B) is supplied from the constant current source (S2). The value of the constant current (II) is

It is set to a certain ratio to the constant current (10) of (S i).

The set value is the current value corresponding to the vicinity of the lower end of the linear region (L) in the characteristic curve (Ci) in Fig. 4, that is, the value in the non-linear region (S _L ). However, it may be a value slightly in the linear area (L). In this example, 11 = 0.310, that is, it is set so as to be exactly equal to the low frequency side starting end of the linear region (L).

In the configuration of the input and output; the base of the modulation signal is collected by run-g is te forming the first Sado对· (Dl) (T2), calibration Li A forming a second differential ¾f (D ₂₎ It is applied as an input to the base of the transistor (T3). Then, the base of another transistor (T4) forming the first differential pair (Dl) has a first fixed bias rejecting at the center level of the carrier. And the source of another transistor (Ti :) forming the second differential pair (D2) has an intermediate level between the peak and peak of the modulated signal. The equivalent of

A fixed bias of 2 is provided. The output is the second differential pair.

From the collector of the transistor (T4) forming (D2)]?

OMPI

WIPO, ν In the basic operation, the transistors (Ti) and (T2) forming the first differential pair (Dl) are always on, and the carrier is driven by the second differential pair (Dl). AM modulation is performed by changing the current with a modulation signal that swings up and down across a fixed bias. This is similar to the prior art. However, since the transistor (Tl) is always supplied with the current of I 1 = 0.310 from the constant current source (S2), the collector of the transistor (Ti) is The current does not flow through the transistors (T3) and (T4) that make up the second differential pair (D2). This is, in other words,

In the non-linear region (SL) in the characteristic diagram of Fig. 4, no current flows through the second differential pair (D2), and the characteristic is 1 = 0 as shown in Fig. 6. 310 and the characteristic curve (C3) that formed the original characteristic curve (C1).

Ni will this Yo, second in 4 view of the characteristic diagram, Roh emissions Linear area (SL) In the second differential pair (D ₂₎ Ba Yi of the first differential pair (Dl) is in any way actuated ¾ physician like Since the constants of the grounding circuit and the circuit (B) are set, it can be seen from the point 0 at 0.3 I 0 on the Vi-I characteristic curve in FIGS. 4 and 6, that is, as shown in FIG. Thus, vi-i can be considered as new coordinates. Here, vi changes from the negative position of the transistor (Ti). 0 This is the input voltage value obtained by subtracting the base potential of the transistor (T2) to which the monotone signal is input]], and i is one of the two that forms the second differential pair (D2) Current flowing through the transistor

Based on these new coordinates v i- i, the modulation rate M = 1 which could not avoid modulation distortion in the prior art shown in Figs. 1 and 2

Calculate the current required to obtain a 75% AM signal.

Let the operating center of the second differential 对 (D2) be 0.210 in the new coordinates (0.5 I 0 in the old coordinates), and let X be the magnitude of the current taken up and down from the operating center with and. In this case, if the maximum value of is expressed by the minimum value of IM, then a current of lM = C 0.2 + x) I o Im = (0.2 · xI o) is secured in the linear region. From this, when X is calculated,

IM- Ιπα 2 x I 0

M = 0.75

lM + Im 0.10

Yo] ?, x = 0.15

Therefore IM = 0.35 I0 m. = 0.05 I0 If linearity is ensured in the range, modulation distortion can be prevented. The linear area (L) is 0.3 in the old coordinate Vi.

IQ ~ 7010] ?, and the new coordinate Vi-i is 0 ~ 0.410, indicating that no modulation distortion occurs even at a modulation rate of M = 75%.

In general, let's give specific design guidelines. First, when the circuit configuration is designed as shown in Fig. 1, the characteristic curve (Ci) in Fig. 4 is obtained. Usually, the operation center is set at the center of the linear region (L) (current value is [Ic]). Assuming that the magnitude of the current value from this operation center to the upper limit (or lower limit) in the linear region (L) is (IL), this (IL) is also determined. Linear area maximum current flowing through the second differential pair (D2) with (L) (IM), the minimum current (Im) ^{is, IM = C 1 c + IL} )

Im = (I C- I L)

And When the upper limit of the modulation factor M between) woo Ru Linear region (L) and M _ma X,

I — Im (I c + II-C I c— II) II

M m ―

IM + Im (I c + I L) + (I cI L) I c current value range (IL) is found either constant, which the (I c)

OMPI WIPO M _max is changed by the force set as above. Therefore, (Ic) is reduced to (Ic-Ii), that is, qualitatively based on the characteristic diagram, the operation start point of the second differential pair is set in the linear region of the AM modulation. new modulation rate M ^ _{ma x} that substantially rather than size and bulk up to it is Ru Kemah. If the desired modulation index and M (M≤ M _'max),

IL

According to the condition of M ^], the current (Ιι,) flowing through the bypass circuit (B), which is a feature of the present invention, is determined.

The circuit shown in Fig. 7 is an IC-based AM modulator specifically designed based on the above guidelines. The same reference numerals as in Fig. 5 indicate the same or corresponding ones. A constant current source connected to the first differential pair (Di) (Si), the door run-g is te (T _5), resistance (R3 by :)?]), Door run-g is te (T5) The base is given a fixed bias. On the other hand, the constant current source (S 2) provided in the bypass circuit (B) includes transistors (T 6), (T 7), (T 8), (Τ9) and a resistor

It consists of a power-rent circuit formed by (R4), (R5), and (I). Even more, the common power line (

+ Vcc) to a relatively large voltage (for example, +9 V). When supplying power, a current mitigation circuit is suitable, but if the voltage is about +5 V, the constant current source (S 2) may have the same configuration as the constant current source (S i). ¾ you, resistance _{(ri), (r 2)} , which is (r 3) is provided, et al or on the creation of the IC resistance. Tic is the terminal of the IC, and the modulated wave power is output from here. This output is, for example, a modulated wave with a modulation rate of 75%, which is obtained by modulating a 92.15 MHz carrier generated by an oscillator circuit with a 04.2 MHz video signal. is there. The modulated wave is mixed with the audio signal and supplied to the antenna terminal of the TV receiver.

Although the above-described embodiment is suitable for an AM modulation circuit built in a converter, the AM modulation circuit having such a configuration is used, for example, in data transmission using a telephone line. It can also be built into MODEM.

In the above description, the basic embodiment of the present invention has been described. However, the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the appended claims by those skilled in the art. can do

ΟΙ, ίΡΙ WIPO ^ _t

Claims

4- Claims

1. A first differential amplifier having a constant current source, and a second differential seal having one of the transistors forming the differential amplifier as a common emitter current source. In an amplitude modulation circuit configured to input a modulation signal to a differential pair and to input a carrier to the other differential pair, a side on which a constant current having a certain ratio to a current of the constant current source flows.振幅 An amplitude modulation circuit, wherein the circuit is connected in parallel with a differential pair having the carrier as an input.

2. The amplitude modulation circuit is incorporated in an integrated circuit.

The amplitude modulation circuit according to claim 1, wherein:

3. The amplitude modulation circuit according to claim 1, wherein the side road surface includes a constant current 葸.

4. The amplitude modulation circuit according to claim 3, wherein said bypass circuit is formed of a series connection of a constant current 葸 and a resistor.

5. The amplitude modulation circuit according to claim 3, wherein the constant current source of the bypass circuit is a current mirror single circuit.