FET monolithic microwave integrated circuit variable attenuator

On a microstripline MMIC, a circuit for attenuating an RF microwave input signal in response to a single control signal, the circuit adapted to receive a first reference voltage the circuit comprising:

• a circuit input port having an input impedance, for receiving the RF microwave input signal from a signal source having a source output impedance:
• the input signal having a frequency range between about 2 GHz and about 20 GHz:
• a circuit output port having an output impedance for supplying an attenuation fraction of the RF microwave input signal to a load having a load input impedance;
• a control port for receiving a single control signal whose amplitude varies the attenuation fraction of the RF microwave input signal reaching the circuit output port;
• a first depletion mode field effect transistor including at least one Schottky gate functioning as an active variable conductance device, having a drain lead coupled to the circuit input port a source lead coupled to the first reference voltage and a gate lead D.C. coupled directly to the control port to receive the single control signal connected to shunt a signal at the RF circuit input port;
• a second depletion mode field effect transistor including at least one Schottky gate functioning as an active variable conductance device having a drain lead coupled to the circuit output port, a source lead coupled to the first reference voltage and a gate lead D.C. coupled directly to the control port to receive the single control signal, connected to shunt a signal at the RF circuit output port;
• a third depletion mode field effect transistor including at least one Schottky gate functioning as an active variable conductance device, having a drain lead coupled to the circuit input port a source lead coupled to the circuit output port and D.C. coupled directly to the control port to receive the single control signal, and having a gate lead coupled to a second reference voltage connected in series with the RF circuit input port and the RF circuit output port;
• the conductance of each field effect transistor being variable in response to the magnitude of the single control signal;
• a frequency dependent D.C. conductive circuit, coupled to the source and drain leads of the third field effect transistor, for shunting a fraction of the input signal across the third field effect transistor where the sum conductance of the frequency dependent circuit and the third field effect transistor is substantially constant over the frequency range of the input signal, thereby extending the frequency response of the attenuator while linearizing circuit attenuation and maintaining a substantially constant input and output impedance;
• a first frequency dependent A.C. conductive circuit coupled in series with an output lead of the first field effect transistor for decoupling the first field effect transistor from a potential at the circuit input port;
• a second frequency dependent A.C. conductive circuit coupled in series with an output lead of the second field effect transistor for decoupling the second field effect transistor from a potential at the circuit output port;
• wherein the magnitude of the components comprising the frequency dependent D.C. conductive circuit and the magnitude of the components comprising the first and second frequency dependent A.C. conductive circuits, together with the magnitude of the stray and parasitic conductance associated with the field effect transistors cause the attenuation circuit to exhibit a shunt resonant frequency measured across the RF circuit input port which is substantially the same as a shunt resonant frequency measured across the RF circuit output port, which is substantially the same as a series resonant frequency measured from the RF circuit input port to the RF circuit output port;
• the varying conductance of the field effect transistors varying the attenuation between the RF circuit input port and the RF circuit output port as the amplitude of the control voltage varies, while the input and output impedance is maintained substantially constant, over a frequency range of about 2-20 GHz.

A microwave system, comprising:

• a microwave amplifier having an amplifier output impedance, capable of amplifying and providing as an amplifier output. RF microwave signals having a frequency range of about 2 GHz to about 20 GHz;
• a circuit on a microstripline MMIC for receiving as an RF microwave input signal the amplifier output and attenuating the amplifier output in response to a single control signal, the circuit adapted to receive a first reference voltage, the circuit comprising:
• a circuit input port having an input impedance, for receiving the RF microwave input signal from a signal source having a source output impedance;
• the input signal having a frequency range between about 2 GHz and about 20 GHz;
• a circuit output port having an output impedance for supplying an attenuation fraction of the RF microwave input signal to a load having a load input impedance;
• a control port for receiving a single control signal whose amplitude varies the attenuation fraction of the RF microwave input signal reaching the circuit output port;
• a first active variable conductance device, having a first output lead coupled to the circuit input port a second output lead coupled to the first reference voltage and a control lead D.C. coupled directly to the control port to receive the single control signal connected to shunt a signal at the RF circuit input port;
• a second active variable conductance device, having a first output lead coupled to the circuit output port, a second output lead coupled to the first reference voltage and a control lead D.C. coupled directly to the control port to receive the single control signal, connected to shunt a signal at the RF circuit output port;
• a third active variable conductance device having a first output lead coupled to the circuit input port, a second output lead coupled to the circuit output port and D.C. coupled directly to the control port to receive the single control signal and a control lead D.C. coupled directly to a second reference voltage connected in series with the RF circuit input port and the RF circuit output port;
• the conductance of each active device being variable in response to the magnitude of the single control signal;
• a frequency dependent D.C. conductive circuit coupled to the first and second output leads of the third conductive device for shunting a fraction of the input signal across the third conductive device, where the sum conductance of the frequency dependent circuit and the third conductive device is substantially constant over the frequency range of the input signal, thereby extending the frequency response of the attenuator while linearizing circuit attenuation and maintaining a substantially constant input and output impedance;
• a first frequency dependent A.C. conductive circuit coupled in series with an output lead of the first active variable conductance device for decoupling the first active device from a potential at the circuit input port, and a second frequency dependent A.C. conductive circuit coupled in series with an output lead of the second active variable conductance devices for decoupling the second active device from a potential at the circuit output port;
• wherein the magnitude of the components comprising the frequency dependent D.C. conductive circuit and the magnitude of the components comprising the first and second frequency dependent A.C. conductive circuits, together with the magnitude of the stray and parasitic conductance associated with the active variable conductive devices, cause the attenuation circuit to exhibit a shunt resonant frequency measured across the RF circuit input port, which is substantially the same as a shunt resonant frequency measured across the RF circuit output port which is substantially the same as a series resonant frequency measured from the RF circuit input port to the RF circuit output port;
• the varying conductance of the active devices varying the attenuation between the RF circuit input port and the RF circuit output port as the amplitude of the control voltage varies, while the input and output impedance is maintained substantially constant over a frequency range of about 2-20 GHz.

On a microstripline MMIC, a circuit for attenuating an RF microwave input signal in response to a single control signal the circuit adapted to receive a first reference voltage the circuit comprising:

• a circuit input port, having an input impedance, for receiving the RF microwave input signal from a signal source having a source output impedance;
• the input signal having a frequency range between 0 and about 20 GHz:
• a circuit output port, having an output impedance, for supplying an attenuation fraction of the RF microwave input signal to a load having a load input impedance;
• first and second control ports for receiving, respectively, first and second control signals whose amplitudes vary the attenuation fraction of the RF microwave input signal reaching the circuit output port;
• the second control signal varying in complementary push-pull relationship to the first control signal;
• a first plurality of active variable conductance devices having a first output lead D.C. coupled directly to the circuit input port a second output lead D.C. coupled directly to the first reference voltage and a control lead D.C. coupled directly to the first control port to receive the first control signal, connected to shunt a signal at the RF circuit input port;
• a second plurality of active variable conductance devices, having a first output lead D.C. coupled directly to the circuit output port, a second output lead D.C. coupled directly to the first reference voltage and a control lead D.C. coupled directly to the first control port to receive the first control signal, connected to shunt a signal at the RF circuit output port;
• a third plurality of active variable conductance devices having a first output, lead D.C. coupled directly to the circuit input port, a second output lead D.C. coupled directly to the circuit output port;
• and
• a control lead D.C. coupled directly to the second control port to receive the second control signal, connected in series with the RF circuit input port and the RF circuit output port;
• the conductance of the first and second plurality of active variable conductance devices being variable in response to the magnitude of the first control signal;
• the conductance of the third plurality of active variable conductance devices being variable in response to the magnitude of the second control signal;
• and
• a frequency dependent D.C. conductive circuit coupled to the first and second output leads of the third conductive device for shunting a fraction of the input signal across the third conductive device where the sum conductance of the frequency dependent circuit and the third conductive device is substantially constant over the frequency range of the input signal thereby extending the frequency response of the attenuator while linearizing circuit attenuation and maintaining a substantially constant input and output impedance;
• the varying conductance of the active devices varying the attenuation between the RF circuit input port and the RF circuit output port as the amplitude of the control voltage varies, while the input and output impedance is maintained substantially constant, over a frequency range of 0 to about 20 GHz.

A microwave system, comprising:

• a microwave amplifier having an amplifier output impedance capable of amplifying and providing as an amplifier output. RF microwave signals having a frequency range of 0 to about 20 GHz;
• a circuit on a microstripline MMIC for receiving as an RF microwave input signal the amplifier output and attenuating the amplifier output in response to a single control signal the circuit adapted to receive a first reference voltage, the circuit comprising:
• a circuit input port having an input impedance for receiving the RF microwave input signal from a signal source having a source output impedance:
• the input signal having a frequency range between about 0 GHz and about 20 GHz:
• a circuit output port having an output impedance for supplying an attenuation fraction of the RF microwave input signal to a load having a load input impedance:
• first and second control ports for receiving;
• respectively, first and second control signals whose amplitudes vary the attenuation fraction of the RF microwave input signal reaching the circuit output port;
• the second control signal varying in complementary push-pull relationship to the first control signal;
• a first plurality of active variable conductance devices having a first output lead D.C. coupled directly to the circuit input port a second output lead D.C. coupled directly to the first reference voltage and a control lead D.C. coupled directly to the first control port to receive the first control signal, connected to shunt a signal at the RF circuit input port;
• a second plurality of active variable conductance devices having a first output lead D.C. coupled directly to the circuit output port, a second output lead D.C. coupled directly to the first reference voltage and a control lead D.C. coupled directly to the first control port to receive the first control signal, connected to shunt a signal at the RF circuit output port:
• a third plurality of active variable conductance devices having a first output lead D.C. coupled directly to the circuit input port, a second output lead D.C. coupled directly to the circuit output port;
• and
• a control lead D.C. coupled directly to the second control port to receive the second control signal connected in series with the RF circuit input port and the RF circuit output port;
• the conductance of the first and second plurality of active variable conductance devices being variable in response to the magnitude of the first control signal;
• the conductance of the third plurality of active variable conductance devices being variable in response to the magnitude of the second control signal;
• and
• a frequency dependent D.C. conductive circuit coupled to the first and second output leads of the third conductive device, for shunting a fraction of the input signal across the third conductive device where the sum conductance of the frequency dependent circuit and the third conductive device is substantially constant over the frequency range of the input signal, thereby extending the frequency response of the attenuator while linearizing circuit attenuation and maintaining a substantially constant input and output impedance;
• wherein the magnitude of the components comprising the frequency dependent D.C. conductive circuit together with the magnitude of the stray and parasitic conductance associated with the active variable conductive devices, cause the attenuation circuit to exhibit a shunt resonant frequency measured across the RF circuit input port which is substantially the same as a shunt resonant frequency measured across the RF circuit output port which is substantially the same as a series resonant frequency measured from the RF circuit input port to the RF circuit output port;
• the varying conductance of the active devices varying the attenuation between the RF circuit input port and the RF circuit output port as the amplitude of the control voltage varies, while the input and output impedance is maintained substantially constant over a frequency range of 0 to about 20 GHz.