Transimpedance amplifiers

A transimpedance amplifier apparatus comprising:

• an input transimpedance amplifier for generating a first voltage based on a current at an input current node;
• a dummy transimpedance amplifier for generating a second voltage based on a first control current;
• and
• a control loop comprising:
• an integrator for generating an integrated value based on the first and second voltages;
• and
• a controller configured to control the first control current, a DC restore current subtracted from the input current node and a gain of the input transimpedance amplifier based on the integrated value, wherein the controller is configured such that:
• for a first range of an input signal magnitude, a first magnitude of the first control current depends on the input signal magnitude and increases with increasing the input signal magnitude whilst a second magnitude of the DC restore current is substantially constant;
• and
• for a second, higher, range of the input signal magnitude, both the first magnitude of the first control current and the second magnitude of the DC restore current depend on the input signal magnitude and the second magnitude of the DC restore current increases with increasing the input signal magnitude while the first magnitude of the first control current reduces.

A transimpedance amplifier apparatus comprising:

• an input transimpedance amplifier for generating a first voltage based on a current at an input current node;
• a dummy transimpedance amplifier for generating a second voltage;
• and
• a control loop configured to control a first control current for the dummy transimpedance amplifier, a DC restore current applied to the input current node and a gain of the input transimpedance amplifier, such that each of the first control current, the DC restore current and the gain vary continuously with an input signal magnitude over at least part of an input dynamic range of the transimpedance amplifier apparatus, wherein the control loop is configured such that:
• for a first range of the input signal magnitude, a first magnitude of the first control current depends on the input signal magnitude and increases with increasing the input signal magnitude whilst a second magnitude of the DC restore current is substantially constant;
• and
• for a second, higher, range of the input signal magnitude, both the first magnitude of the first control current and the second magnitude of the DC restore current depend on the input signal magnitude and the second magnitude of the DC restore current increases with increasing the input signal magnitude while the first magnitude of the first control current reduces.