Patent ID: 7106095

Claim:
A circuit for mixing frequencies, the circuit comprising: a mixer for receiving a first input signal having a first frequency and a second input signal having the first frequency, the first input signal having an inverted phase with respect to the second input signal, the mixer for mixing a local oscillating signal having a second frequency with the first and second input signals to output first and second output signals to first and second output terminals, respectively, the first output signal having a third frequency corresponding to a first difference between the second and first frequency, the second output signal having the third frequency; a first pull-up resistor for pulling up the first output terminal; a second pull-up resistor for pulling up the second output terminal; and a difference compensation circuit, coupled with the first and second pull-up resistors, for compensating for a second difference between resistance measured from the first and second pull-up resistors in response to a control signal having (k+1) bits, wherein the difference compensation circuit comprises: a first resistor for transforming a first resistance value into a fine resistance value having 2 n steps in response to n lower bits of the k bits of the control signal, the first resistance value being measured at the first pull-up resistor, k being equal to m plus n, m and n being positive integers; and a second resistor for transforming a second resistance value into a coarse resistance value having 2 m steps in response to m upper bits of k bits of the control signal, the second resistance value being measured at the second pull-up resistor.