JPS593894B2 - phase modulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates generally to phase modulation circuits, and more particularly to improvements in phase modulation circuits that convert an input analog signal into a pulse width modulation (PWM) signal and then into a pulse phase modulation (PPM) signal. .

An example of a conventional PWM-PPM conversion phase modulation circuit is shown in the first example.
As shown in the figure.

In FIG. 1, 11 is an analog modulation signal terminal, and 12 is a carrier wave input terminal, into which a triangular waveform of a constant level is input.

The modulated signal and the carrier wave are compared by a voltage comparator 13, and an instantaneous modulated PWM signal is obtained at its output.

Reference numeral 14 denotes a monostable multi-by-break that is triggered by the rising edge of a human input signal, and a capacitor 5 and a resistor 16 that determine the time constant are set so that the duty cycle of the output pulse is 50%.

FIG. 2 is a voltage waveform diagram showing the operation of FIG.
Each symbol indicates an operating waveform at a location with the same symbol in FIG.

As understood from FIG. 2, the falling edge of the PWM signal deviates by up to ±90° in proportion to the magnitude of the modulation signal.

Therefore, the output of the monostable piebreak is phase modulated up to ±90°.

However, since the time constant of the multi-by-break 14 is determined by the charging and discharging of the CR, fluctuations in the pulse width of the multi-by-break become phase noise, which has the disadvantage that S/N becomes a problem depending on the application.

Therefore, the present invention aims to improve the above-mentioned drawbacks of the prior art, and its purpose is to provide a phase modulation circuit with good S/H without reducing the degree of phase modulation. In a phase modulation circuit that converts the pulse width modulation signal into a pulse width modulation signal, converts the pulse width modulation signal into a pulse phase modulation signal, and outputs the pulse width modulation signal, two-phase pulses corresponding to the input analog signal having carrier waves having a mutually opposite phase relationship are used. means for generating a width modulation signal; a pair of master-slave flip-flops triggered by each pulse width modulation signal; and a complementary signal at the J and J terminals of the flip-flops having a frequency divided carrier wave. and means for providing a phase modulated output by exclusive ORing each output of the pair of flip-flops.

Examples will be described below with reference to the drawings.

FIG. 3 is a block diagram of the first embodiment of the phase modulation circuit according to the present invention, in which 31 is a modulation signal input terminal, 32 is a carrier wave input terminal, and the triangular wave signal from 32 is connected to a wideband amplifier 33 having a differential output. The signals are connected to the reference terminals of two high-speed voltage comparators 34 to 35, respectively.

The comparison terminals of the comparators are given modulated signals in the same phase, and their outputs are provided with two signals in which only the phase of the carrier wave is reversed.
A phase PWM signal is obtained.

They can be frequency-divided into J- by flip-flops 37 and 38 to obtain a PPM signal with a frequency of 1 of a carrier wave with small phase noise, and they can be divided by exclusive OR.
By calculating the exclusive OR using the gate 42 (exclusive OR), as can be understood from the voltage waveform diagram of the operation explanation in FIG. A 90° PPM signal can be obtained.

The waveforms in FIG. 4 show the operating waveforms at the same numbered points in FIG. 3, 5' and 6 are carrier wave signals having mutually opposite phases, and 7 is an analog modulation signal.

Further, in FIG. 4, the output waveform (2) and the spider pulse width of the exclusive OR circuit are shown as changing, but this is for the purpose of making the operation easier to understand.

In other words, this is because the modulation frequency and the carrier frequency are shown as being close to each other, and the illustration shows that a phase modulation component actually occurs in the pulse width modulation stage, and also because the graph representation is essentially on the same time axis. This is because it is impossible to represent a phase change without a frequency change using a constant pulse width.

In reality, the modulation frequency is sufficiently lower than the carrier frequency, so that the pulse width of the output waveform of the exclusive OR circuit does not vary with the amplitude of the analog signal.

This relationship can be illustrated as shown in FIG. 6, for example.

(Reference numbers are the same as in Figure 4.) Since the modulated wave ■ has a sufficiently lower frequency than the carrier wave ■■, it can be drawn as an almost straight line, and therefore the output waveform ■ of the exclusive OR circuit has a varying pulse width. It becomes a 50% duty circle without doing anything.

If the level of the modulated wave (■) moves downward, the output waveform of the exclusive OR circuit will simply shift to the left, but its pulse width will not change.

The J- terminal of the J- flip-flop is connected to Q and Q of the T-flip-flop 41 which shapes the waveform by the input carrier voltage comparator 36 and divides the frequency by 100, so the phase of the frequency division is inverted. There is no possibility.

J- to flip-flop 39.40 and exclusive
The circuit using the ive OR gate 43 is exactly the same as the circuit using the J- flip-flops 37 and 38 and the exclusive OR gate 42, but since inverters 44 and 45 are connected to its inputs, it is triggered at the rising edge of the PWM signal.

That is, in master-slave operation, the J- flip-flops 39 and 40 read the output of the T-flip-flop 41 at the falling edge of the PWM signal (the rising edge of the T terminal), and output it to Q and Q at the rising edge.

In this way, a PPM signal having a phase shift in the opposite direction to that of the output terminal 46 is obtained at the output terminal 47.

As explained above, in the first embodiment, since the flip-flop does not use the CR time constant, the phase noise is very small and even if the carrier frequency is changed over a wide range,
It has the advantage of working.

In the first embodiment, the phase of the carrier wave is inverted to perform two-phase pulse width modulation, but it can also be constructed by inverting the phase of the modulation signal.

In that case, to invert one of the PWM signal outputs, an inverter is connected to the output, or the input terminals of the voltage comparator are reversed as shown in FIG.

Further, in the first embodiment, a two-phase PPM modulated signal was obtained, but the effect of the present invention is the same in the case of a single phase as shown in FIG.

In FIG. 5, 51 is a modulation signal input terminal, 52 is a carrier wave input terminal, 53 is a phase inverting transformer with a center-tapped secondary winding, 54 to 56 are voltage comparators, and 57 is a T
Flip-flops, 58 and 59 are master slave J
- flip-flop, 60 is exclusive
OR gate 61 is an output terminal.

The present invention has the advantage of having small phase noise and being able to obtain a positive/negative symmetrical phase shift, and can be used for PM generation in an AM modulator using PM-AM conversion such as the AMPLI-PHASE method.

[Brief explanation of the drawing]

Figure 1 is an example of a conventional phase modulation circuit, Figure 2 is an operational waveform diagram of the circuit in Figure 1, Figure 3 is a block diagram of a phase modulation circuit according to the present invention, and Figure 4 is a diagram of the circuit in Figure 3. FIG. 5 is a block diagram of another embodiment of the phase modulation circuit according to the present invention, and FIG. 6 is an operational waveform diagram of the circuit of FIG. 3. 11...Modulation signal input terminal, 12...
Carrier wave (triangular wave) input terminal, 13... Voltage comparator, 14... Monostable multivib break, 15... Capacitor, 16... Resistor, 17. ...Output terminal, 31...Modulation signal input terminal, 32...Carrier wave input terminal, 33
... Differential amplifier, 34-36 ... Voltage comparator, 37-40 ... Master slave J
- flip-flop, 41...T flip-flop, 42-43...EX/OR gate,
44, 45...Inverter, 46-47...
...output terminal, 51...modulation signal input terminal,
52... Carrier wave input terminal, 53... Phase inversion transformer, 54, 55, 56... Voltage comparator, 57... T flip-flop, 58- 5
9...Flip-flop to master/slave J-, 60...EX-OR gate, 61... Song output terminal.

Claims (1)

[Claims] 1. In a phase modulation circuit that converts an analog signal into a pulse width modulation signal, converts the pulse width modulation signal into a pulse phase modulation signal, and outputs the signal, the circuit has carrier waves having mutually opposite phases and corresponds to the input analog signal. means for generating two-phase pulse-width modulated signals, a pair of master slave flip-flops triggered by each pulse-width modulated signal, and a carrier wave at the J and terminals of the flip-flops;
means for applying a complementary signal divided to a frequency of 1;
and means for providing a phase modulation output by exclusive OR of each output of a pair of flip-flops.