Mixer circuit with balanced frequency mixer with varactor diodes

A local coil arrangement for a magnetic resonance apparatus comprising:

• a reception coil that receives a magnetic resonance signal and produces a first input signal therefrom exhibiting a first input frequency;
• a signal generator that generates a second input signal having an input frequency that is a multiple of said first input frequency;
• a balanced frequency mixer having a first input connected to said coil to receive said first input signal therefrom, and a second input connected to said signal generator to receive said second input signal therefrom;
• said balanced frequency mixer comprising at least two amplifier elements each formed by a veractor diode, that mix said first and second input signals with each other into a mix signal comprising a first signal component and a second signal component, said first signal component exhibiting a first component frequency that is a sum of said first and second input frequencies, and said second signal component exhibiting a second component frequency that is a difference between said first and second input frequencies;
• said balanced frequency mixer having an output at which at least one of said first and second signal components of said mix signal is tapped;
• said second input and said output being decoupled from each other;
• and
• each of said veractor diodes having an adjustment circuit connected in parallel therewith that adjusts an operating point of that veractor diode.