Pulse width modulator for AM-RF transmitter

• US 4,896,372 A
• Filed: 02/25/1986
• Issued: 01/23/1990
• Est. Priority Date: 02/25/1986
• Status: Expired due to Term

• Current Assignee: DRS Broadcast Technology Incorporated
• Original Assignee: Varian Associates, Inc. (Siemens AG)
• Inventors: Weaver, Bryan A.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US06/832,630
• Time in Patent Office: 1,428 Days
• Field of Search: 375/22, 375/23, 455/108, 330/10, 332/9, 332/109-111
• US Class Current: 455/108
• CPC Class Codes: H03C 1/16 by means of discharge device having at least three electrodes H03C1/28 - H03C1/34, H03C1/50, H03C1/52, H03C1/62 take precedence
• CPC Class Codes: H03K 7/08 Duration or width modulation ; Duty cycle modulation

Abstract

An RF-AM transmitter of the type including a power pulse amplifier driving an RF amplifier with a modulating voltage via a low pass filter includes a pulse width modulator for deriving variable frequency pulses having a frequency that is a direct function of an RMS like function of the amplitude and frequency of an information source; the width of the pulses is determined by the instantaneous amplitude of the information signal source. The pulse width modulator includes a constant amplitude, variable frequency triangular wave voltage controlled oscillator responsive to a DC signal representing the frequency and amplitude of the information source. In response to amplitude crossovers between the variable frequency triangular wave and the information source, transitions in the pulse width modulated wave are derived.

Claims

1. A radio transmitter for transmitting an RF carrier amplitude modulated by an information signal comprising a pulse width modulator responsive to the information signal for deriving a pulse width modulated signal having pulses with widths representing the instantaneous amplitude of the information signal and a frequency that is a direct function of the frequency and an RMS like function of the amplitude of the information signal, the RMS like function including the integral of a single polarity function of the information signal, a power amplifier responsive to the pulse width modulated signal including a power amplifying element connected to a DC power supply terminal, the power amplifying element deriving a high power signal that is a substantial replica of the pulse width modulated signal, a low pass filter responsive to the high power signal for deriving a signal that is a substantial replica of the information signal, and an RF amplifier having an anode-cathode path in DC circuit with the DC power supply terminal via the low pass filter and the power amplifying element.

2. The transmitter of claim 1 wherein the pulse width modulator includes a variable frequency oscillator for deriving an output wave having a constantly changing amplitude, means responsive to the information signal for supplying a DC signal having a magnitude that changes as a function of frequency and the RMS like function of the amplitude of the information signal to the oscillator, the oscillator responding to the DC signal so the oscillator output frequency increases as the frequency and the RMS like function of the amplitude of the information signal increase.

3. The transmitter of claim 2 wherein the pulse width modulated signal is a bilevel signal, the modulator further including means for controlling transitions of the bilevel signal so that each transition in said bilevel signal occurs in synchronism with each change in the relative polarity of the information signal and the output wave.

4. The transmitter of claim 2 wherein the modulator includes rectifier means, means for AC coupling a signal indicative of the information signal to the rectifier means, and integrator means responsive to an output signal of the rectifier means for deriving the DC signal that is supplied to the oscillator.

5. The transmitter of claim 2 wherein the modulator includes an operational amplifier, a capacitor series connected between a source of said information signal and an input of said operational amplifier for differentiating said information signal and for coupling said differentiated signal to said operational amplifier, a feedback path connected to said operational amplifier including means for causing said operational amplifier to block portions of said differentiated signal having a first polarity and for deriving a replica of portions of said differentiated signal having a second polarity, means for linearly combining a replica of said differentiated signal and an output signal of the operational amplifier to derive a unidirectional signal having a waveshape that is a replica of both polarities of said differentiated signal, and means for integrating the unidirectional signal to derive the DC signal that is supplied to the oscillator.

6. The transmitter of claim 2 wherein the output wave has a triangular shape as a function of amplitude and time.

7. An AM radio transmitter for transmitting an RF carrier amplitude modulated by an information signal having variable amplitude and frequency characteristics comprising a pulse width modulator responsive to the information signal for deriving a pulse width modulated signal having pulses with widths representing the instantaneous amplitude of the information signal and a variable frequency that is a function of at least one of said characteristics of the information signal, said modulator including a variable frequency oscillator for deriving an output wave having a constantly changing amplitude, means responsive to the information signal for supplying a DC signal having a magnitude that changes as a function of at least one of said characteristics of the information signal to the oscillator to control the frequency of the output wave, the pulse width modulated signal being a bilevel signal, the modulator including means for controlling transitions of the bilevel signal so that each transition in said bilevel signal occurs in synchronism with each change in the relative polarity of the information signal and the oscillator output wave, and means responsive to a smoothed replica of the pulse width modulated bilevel signal for deriving the RF amplitude modulated carrier.

8. The transmitter of claim 7 wherein the function for the frequency of the pulses is a direct function of the amplitude of said information signal so that as the amplitude of the information signal increases the frequency of the pulses increases.

9. The transmitter of claim 8 wherein the modulator includes rectifier means, means for coupling a signal responsive to the information signal to the rectifier means, and integrator means responsive to an output signal of the rectifier means for deriving the DC signal that is supplied to the oscillator.

10. The transmitter of claim 8 wherein the function for the frequency of the pulses is a direct function of the frequency of said information signal so that as the frequency of the information signal increases the frequency of the pulses increases.

11. The transmitter of claim 7 wherein the output wave has a triangular shape as a function of amplitude and time.

12. The radio transmitter of claim 7 wherein the DC control signal deriving means includes an operational amplifier, a capacitor series connected between a source of said information signal and an input of said operational amplifier for differentiating said information signal and for coupling said differentiated signal to said operational amplifier, a feedback path connected to said operational amplifier including means for causing said operational amplifier to block portions of said differentiated signal having a first polarity and for deriving a replica of portions of said differentiated signal having a second polarity, means for linearly combining a replica of said differentiated signal and an output signal of the operational amplifier to derive a unidirectional signal having a waveshape that is a replica of both polarities of said differentiated signal, and means for integrating the unidirectional signal to derive the DC signal that is supplied to the oscillator.

13. The transmitter of claim 7 wherein the function for the frequency of the pulses is a direct function of the frequency of said information signal so that as the frequency of the information signal increases the frequency of the pulses increases.

14. A source of pulse width modulated pulses having a variable frequency that is a function of an AC information signal comprising a variable frequency voltage controlled oscillator for deriving a variable frequency output wave having a continuously varying amplitude, rectifying means responsive to the AC information signal for deriving a DC control voltage for the oscillator, the oscillator responding to the DC control voltage to derive the variable frequency output wave, and means responsive to the AC information signal and the output wave for deriving a variable frequency bilevel pulse width modulated signal having pulse widths that are a function of the instantaneous amplitude of the AC input signal so the frequency of the pulse width modulated signal increases as the amplitude of the AC signal increases and vice versa, said last named means including means for controlling transitions of the bilevel signal so that each transition in said bilevel signal occurs in synchronism with each change in the relative polarity of the information signal and the continuously varying amplitude output wave.

15. The source of claim 14 wherein the DC control signal deriving means includes means responsive to the AC information signal for causing the oscillator frequency to vary directly with the amplitude and frequency of the AC information signal.

16. The source of claim 14 wherein the DC control signal deriving means includes means responsive to the AC information signal for causing the oscillator frequency to vary directly with the amplitude and frequency of the AC information signal, the DC control signal deriving means including an operational amplifier, a capacitor series connected between a source of said information signal and an input of said operational amplifier for differentiating said information signal and for coupling said differentiated signal to said operational amplifier, a feedback path connected to said operational amplifier including means for causing said operational amplifier to block portions of said differentiated signal having a first polarity and for deriving a replica of portions of said differentiated signal having a second polarity opposite to the first polarity, means for linearly combining a replica of said differentiated signal and an output signal of the operational amplifier to derive a unidirectional signal having a waveshape that is a replica of both polarities of said differentiated signal, and means for integrating the unidirectional signal to derive the DC signal that is supplied to the oscillator.

17. The source of claim 14 wherein the DC control signal deriving means includes an operational amplifier, impedance means connected between a source of said information signal and an input of said operational amplifier for feeding a signal that is a first function of the information signal to the input of said operational amplifier, a feedback path connected to said operational amplifier including means for causing said operational amplifier to block portions of the input signal of the operational amplifier having a first polarity and for deriving a replica of portions of the input signal of the operational amplifier having a second polarity, means for linearly combining a replica of said signal that is a function of the information signal and an output signal of the operational amplifier to derive a unidirectional signal having a waveshape that is a replica of both polarities of said differentiated signal, and means for integrating the unidirectional signal to derive the DC signal that is supplied to the oscillator.

18. The source of claim 14 wherein the DC control signal deriving means includes means responsive to the AC information signal for causing the oscillator frequency to vary directly with the amplitude and frequency of the AC information signal.

19. The source of claim 18 wherein the DC control signal deriving means includes an operational amplifier, impedance means connected between a source of said information signal and an input of said operational amplifier, a feedback path for said operational amplifier including means for causing said operational amplifier to block portions of the input signal of the operational amplifier having a first polarity and for deriving a replica of portions of the input signal of the operational amplifier having a second polarity, means for linearly combining a replica of said differentiated signal and an output signal of the operational amplifier to derive a unidirectional signal having a waveshape that is a replica of both polarities of said differentiated signal, and means for integrating the unidirectional signal to derive the DC signal that is supplied to the oscillator.

20. The source of claim 14 wherein the DC control signal deriving means includes rectifier means, means for coupling a signal indicative of the information signal to the rectifier means, and integrator means responsive to an output signal of the rectifier means for deriving the DC signal that is supplied to the oscillator.

21. The source of claim 14 wherein the DC control signal deriving means includes an operational amplifier, a capacitor series connected between a source of said information signal and an input of said operational amplifier for differentiating said information signal and for coupling said differentiated signal to said operational amplifier, a feedback path connected to said operational amplifier including means for causing said operational amplifier to block portions of said differentiated signal having a first polarity and for deriving a replica of portions of said differentiated signal having a second polarity, means for linearly combining a replica of said differentiated signal and an output signal of the operational amplifier to derive a unidirectional signal having a waveshape that is a replica of both polarities of said differentiated signal, and means for integrating the unidirectional signal to derive the DC signal that is supplied to the oscillator.

22. The source of claim 14 wherein the DC control signal deriving means includes an operational amplifier, impedance means connected between a source of said information signal and an input of said operational amplifier for feeding a signal that is a first function of the information signal to the input of said operational amplifier, a feedback path connected to said operational amplifier including means for causing said operational amplifier to block portions of the input signal of the operational amplifier having a first polarity and for deriving a replica of portions of the input signal of the operational amplifier having a second polarity, means for linearly combining a replica of said signal that is a function of the information signal and an output signal of the operational amplifier to derive a unidirectional signal having a waveshape that is a replica of both polarities of said differentiated signal, and means for integrating the unidirectional signal to derive the DC signal that is supplied to the oscillator.

23. The transmitter of claim 14 wherein the output wave having a continuously varying amplitude is a triangular wave as a function of amplitude and time.

24. A radio transmitter for transmitting an RF carrier amplitude modulated by an information signal comprising a pulse width modulator responsive to the information signal for deriving a pulse width modulated signal having pulses with widths representing the instantaneous amplitude of the information signal and a frequency that is a direct function of an RMS like function of the amplitude of the information signal so that as the amplitude of the RMS like function increases the frequency of the pulse width modulated signal increases and vice versa, the RMS like function including the integral of a single polarity function of the information signal, a power amplifier responsive to the pulse width modulated signal including a power amplifying element connected to a DC power supply terminal, the power amplifying element deriving a high power signal that is a substantial replica of the pulse width modulated signal, a low pass filter responsive to the high power signal for deriving a signal, and an RF amplifier having an anode-cathode path in DC circuit with the DC power supply terminal via the low pass filter and the power amplifying element.

25. The transmitter of claim 24 wherein the pulse width modulator includes a variable frequency oscillator for deriving an output wave having a constantly changing amplitude, means responsive to the information signal for supplying a DC signal having a magnitude that changes as a function of the RMS like function of the amplitude of the information signal to the oscillator, the oscillator responding to the DC signal so the oscillator output frequency increases as the RMS like function of the amplitude of the information signal increases.

26. The transmitter of claim 25 wherein the pulse width modulated signal is a bilevel signal, the modulator further including means for controlling transitions of the bilevel signal so that each transition in said bilevel signal occurs in synchronism with each change in the relative polarity of the information signal and the output wave.

27. The transmitter of claim 25 wherein the modulator includes rectifier means, means for AC coupling a signal indicative of the information signal to the rectifier means, and integrator means responsive to an output signal of the rectifier means for deriving the DC signal that is supplied to the oscillator.

28. The transmitter of claim 25 wherein the modulator includes an operational amplifier, a capacitor series connected between a source of said information signal and an input of said operational amplifier for differentiating said information signal and for coupling said differentiated signal to said operational amplifier, a feedback path connected to said operational amplifier including means for causing said operational amplifier to block portions of said differentiated signal having a first polarity and for deriving a replica of portions of said differentiated signal having a second polarity, means for linearly combining a replica of said differentiated signal and an output signal of the operational amplifier to derive a unidirectional signal having a waveshape that is a replica of both polarities of said differentiated signal, and means for integrating the unidirectional signal to derive the DC signal that is supplied to the oscillator.

29. The transmitter of claim 25 wherein the output wave has a triangular shape as a function of amplitude and time.

30. The transmitter of claim 24 wherein said pulse width modulator includes means responsive to the information signal for deriving a signal having a magnitude that is directly related to the RMS like function of the amplitude of the information signal.

31. The transmitter of claim 24 wherein the RMS like function is the average value of a rectified replica of the information signal.

32. The transmitter of claim 24 wherein the RMS like function is the average value of a fullwave rectified replica of the information signal.

33. An AM radio transmitter for transmitting an RF carrier amplitude modulated by an information signal having variable amplitude and frequency characteristics comprising a pulse width modulator responsive to the information signal for deriving a pulse width modulated signal having pulses with widths representing the instantaneous amplitude of the information signal and a frequency that is a direct function of the amplitude of the information signal so that as the amplitude of the information signal increases the frequency of the pulse width modulated signal increases and vice versa, said modulator including a variable frequency oscillator for deriving an output wave having a constantly changing amplitude, means responsive to the information signal for supplying a DC signal having a magnitude that changes as a function of one of said characteristics of the information signal to the oscillator to control the frequency of the output wave in accordance with said function, the pulse width modulated signal being a bilevel signal, the modulator including means for controlling transitions of the bilevel signal so that each transition in said bilevel signal occurs in response to changes in the relative polarity of the information signal and the oscillator output wave, and means responsive to a smoothed replica of the pulse width modulated bilevel signal for deriving the RF amplitude modulated carrier.

34. The source of claim 33 wherein the DC control signal deriving means includes an operational amplifier, a capacitor series connected between a source of said information signal and an input of said operational amplifier for differentiating said information signal and for coupling said differentiated signal to said operational amplifier, a feedback path connected to said operational amplifier including means for causing said operational amplifier to block portions of said differentiated signal having a first polarity and for deriving a replica of portions of said differentiated signal having a second polarity, means for linearly combining a replica of said differentiated signal and an output signal of the operational amplifier to derive a unidirectional signal having a waveshape that is a replica of both polarities of said differentiated signal, and means for integrating the unidirectional signal to derive the DC signal that is supplied to the oscillator.

35. An AM radio transmitter for transmitting an RF carrier amplitude modulated by an information signal comprising a pulse width modulator responsive to the information signal for deriving a pulse width modulated signal having pulses with widths representing the instantaneous amplitude of the information signal and a variable frequency that is a function of the information signal so that as the amplitude of the information signal increases the frequency of the pulse width modulated signal increases and as the frequency of the information signal increases the frequency of the pulse width modulated signal increases, and means responsive to a smoothed replica of the pulse width modulated signal for deriving the RF amplitude modulated carrier.