Analog multiplier circuit

Claim 2

An analog multiplier circuit comprising - a differential amplifier for producing a first and a second current flowing through a summing node thereof, the difference between the first and the second current varying in response to a first electrical input signal; and - a signal current source coupled to be responsive to a second electrical input signal for controlling the current flowing through the summing node; wherein - the difference between the first and the second current varies substantially in proportion to the product of the first and the second electrical input signal; characterized in that, for improving accuracy in the multiplication of varying electrical signals, there is provided - a direct current source (17) connected to the summing node for delivering a direct current thereto; and - AC coupling means (13, 15) for AC coupling the signal current source to the summing node.

Claim 3

A circuit as in claim 1, characterized in that the AC coupling means comprises a resistor (15) connected to convert the current of the signal current source (7) into a signal voltage and a capacitor (13) connected to couple a signal current to the summing node in response to the signal voltage.

Claim 4

A circuit as in claim 1 or 2, characterized in that - the differential amplifier (30) comprises a first transistor (9) and a second transistor (10) and - the summing node is a connection of the emitter of the first transistor (9) to the emitter of the second transistor (10).

Claim 5

An analog multiplier circuit comprising - a first differential amplifier for producing a first and a second current flowing through a summing node thereof, the difference between the first and the second current varying in response to a first electrical input signal; - a second differential amplifier for producing a third and a fourth current flowing through a summing node thereof, the difference between the third and the fourth current varying in response to the inverse of the first electrical input signal; - a first signal current source coupled to be responsive to a second electrical input signal for controlling the current flowing through the summing node of the first differential amplifier; and - a second signal current source coupled to be responsive to the inverse of the second electrical input signal for controlling the current flowing through the summing node of the second differential amplifier; wherein - the difference between the sum of the first and the third current and the sum of the second and the fourth current varies substantially in proportion to the product of the first and the second electrical input signal; characterized in that, for improving accuracy in the multiplication of varying electrical signals, there is provied - a first direct current source (17) connected to the summing node of the first differential amplifier (30) for delivering a first direct current thereto; - a second direct current source (18) coupled to the summing node of the second differential amplifier (40) for delivering a second direct current thereto; - first AC coupling means (13, 15) for AC coupling the first signal current source (7) to the summing node of the first differential amplifier (30); and - second AC coupling means (14, 16) for AC coupling the second signal current source (8) to the summing node of the second differential amplifier (40).

Claim 6

An analog multiplier circuit comprising - a first differential amplifier for producing a first and a second current flowing through a summing node thereof, the difference between the first and the second current varying in response to a first electrical input signal; - a second differential amplifier for producing a third and a fourth current flowing through a summing node thereof, the difference between the third and the fourth current varying in response to the inverse of the first electrical input signal; - a first signal current source coupled to be responsive to a second electrical input signal for controlling the current flowing through the summing node of the first differential amplifier; and - a second signal current source coupled to be responsive to the inverse of the second electrical input signal for controlling the current flowing through the summing node of the second differential amplifier; wherein - the difference between the sum of the first and the third current and the sum of the second and the fourth current varies substantially in proportion to the product of the first and the second electrical input signal; characterized in that, for improving accuracy in the multiplication of varying electrical signals, there is provied - a first direct current source (17) connected to the summing node of the first differential amplifier (30) for delivering a first direct current thereto; - a second direct current source (18) coupled to the summing node of the second differential amplifier (40) for delivering a second direct current thereto; - first AC coupling means (13, 15) for AC coupling the first signal current source (7) to the summing node of the first differential amplifier (30); and - second AC coupling means (14, 16) for AC coupling the second signal current source (8) to the summing node of the second differential amplifier (40).

Claim 7

A circuit as in claim 4, characterized in that - the first AC coupling means (13, 15) comprises a first resistor (15) connected to convert the current of the first signal current source (7) into a first signal voltage, and a first capacitor (13) connected to couple a first signal current to the summing node of the first differential amplifier (30) in response to the first signal voltage; and - the second AC coupling means (14, 16) comprises a second resistor (16) connected to convert the current of the second signal current source (8) into a second signal voltage, and a second capacitor (14) connected to couple a second signal current to the summing node of the second differential amplifier (40) in response to the second signal voltage.

Claim 8

A circuit as in claim 4 or 5, characterized in that - the first signal current source is a first current output port of a third differential amplifier (60); and - the second signal current source is a second current output port of the third differential amplifier (60).

Claim 9

A circuit as in one of claims 4 through 6, characterized in that - the first differential amplifier (30) and the second differential amplifier (40) each comprise a first transistor (9, 11) and a second transistor (10, 12); and - each summing node is a connection of the emitter of the respective first transistor (9,11) to the emitter of the respective second transistor (10, 12).