METHOD AND APPARATUS FOR GENERATING A RADIO FREQUENCY PULSE
The invention is a method and circuit for generating a pulsed periodic signal comprising a sub-harmonic mixer and a control circuit adapted to cause the output signal of the sub-harmonic mixer to be pulsed.
1 . A circuit for generating a pulsed periodic output signal comprising:
a sub-harmonic mixer; and
a control circuit adapted to cause the output signal of the sub-harmonic mixer to be pulsed.
2 . The circuit of claim 1 wherein the control circuit is coupled to the sub-harmonic mixer and is adapted to turn the sub-harmonic mixer on and off at a pulse rate.
3 . The circuit of claim 1 wherein the sub-harmonic mixer comprises:
a first multiplier coupled to multiply a first periodic input signal with a second periodic input signal and generate an output signal; and
a second multiplier coupled to multiply the output signal of the first multiplier with a third periodic input signal, the third periodic input signal having the same frequency as and being 90° out of phase with the second input signal, and generating an output signal comprising the pulsed periodic output signal.
4 . The circuit of claim 3 wherein the first and second multipliers comprise Gilbert multipliers.
5 . The circuit of claim 4 wherein the sub-harmonic mixer comprises at least one transistor and wherein the control circuit comprises circuitry that provide a bias voltage signal to the at least one transistor that alternately biases the at least one transistor on and off at the pulse rate.
6 . The circuit of claim 3 wherein the first and second multipliers comprise passive circuit components.
7 . The circuit of claim 3 wherein the sub-harmonic mixer is fabricated in CMOS.
8 . The circuit of claim 1 wherein the first periodic input signal has the same frequency as the second and third periodic input signals.
9 . The circuit of claim 8 wherein the pulsed periodic output signal has a frequency of three times the frequency of the first, second, and third periodic input signals.
10 . The circuit of claim 9 wherein the first, second, and third periodic input signals are continuous wave sinusoidal signal.
11 . The circuit of claim 8 further comprising a single local oscillator for generating the first, second, and third periodic input signals.
12 . The circuit of claim 11 further comprising a quadrature generator coupled between the local oscillator and the sub-harmonic mixer for generating the second and third input signals from the local oscillator.
13 . A radar system comprising the circuit of claim 1 wherein said pulsed periodic output signal is a radar output signal of the radar system.
14 . A circuit for generating a pulsed periodic output signal that is pulsed at a pulse rate comprising:
a sub-harmonic mixer coupled to mix first, second, and third sinusoidal input signals, wherein the second and third sinusoidal input signals have the same frequency and are 90° out of phase with each other, and generate a sinusoidal output signal having a frequency at the sum of the frequencies of the first, second, and third input signals; and
a control circuit adapted to cause the output signal of the sub-harmonic mixer to be pulsed at the pulse rate.
15 . The circuit of claim 14 wherein the sub-harmonic mixer comprises active circuit components including at least one transistor and wherein the control circuit comprises a current source adapted to generate a current that biases the at least one transistor on and off at the pulse rate.
16 . The circuit of claim 14 wherein the control circuit turns the sub-harmonic mixer on and off at the pulse rate.
17 . The circuit of claim 14 wherein the control circuit comprises a switch coupled to pulse the first input signal at the pulse rate.
18 . The circuit of claim 14 wherein the control circuit comprises a switch coupled to pulse the second and third input signals at the pulse rate.
19 . The circuit of claim 18 further comprising:
a local oscillator for generating a sinusoidal local oscillator signal; and
a quadrature generator coupled to receive the local oscillator signal and generate the second and third input signals from the local oscillator signal;
wherein the switch is coupled to the local oscillator signal to pulse the local oscillator signal into the quadrature generator.
20 . The circuit of claim 15 wherein the sub-harmonic mixer comprises only passive circuit components.
21 . A method of generating a pulsed radio frequency output signal comprising the steps of:
multiplying a first periodic input signal at a first frequency with a second periodic input signal at a second frequency to generate an intermediate signal;
multiplying the intermediate signal with a third periodic input signal having the second frequency and being 90° out of phase with the second input signal to generate an output signal at a frequency of the sum of the frequencies of the first, second, and third periodic input signals; and
pulsing the output signal.
22 . The method of claim 21 wherein the step of pulsing the output signal comprises:
pulsing the first periodic input signal.
23 . The method of claim 21 wherein the step of pulsing the output signal comprises:
pulsing the second and third periodic input signals.
24 . The method of claim 21 wherein the step of pulsing the output signal comprises:
pulsing the step of multiplying the periodic signal and pushing the step of the multiplying the intermediate signal on and off simultaneously.
25 . A method of generating a pulsed radio frequency output signal comprising the steps of:
mixing a first periodic input signal at a first frequency with a second periodic input signal and a third periodic input signal in a sub-harmonic mixer, the second and third input signals being in quadrature at a second frequency; and
pulsing the sub-harmonic mixer on and off.