Double balanced mixer with switching pairs complementary to each other

摘要

A double balanced mixer has a DC detection circuit connected to receive the output of the mixer core. The detected level is applied to adjust the duty cycle of the transistors of the mixer core. In one example, this adjusting level is added to the local oscillator signals that are applied to the core. In another example, the level is applied to adjust the threshold of the transistors of the mixer core. In a further example, the duty cycle of the local oscillator signals is adjusted before it is applied to the mixer core Also provided is an input stage for a double balanced mixer core, which comprises a transistor having a low pass filter as a feedback circuit.

主权项

1. A double balanced mixer comprising:
a mixer core having a radio frequency input port, a local oscillator input port, an output port, the mixer core comprising a first pair of switching transistors, each connected to switch, in anti-phase to the other of the first pair of switching transistors, in response to the local oscillator signals, which first pair is connected to switch radio frequency signals present on a first terminal, common to the first pair, of the radio frequency input port of the mixer core, and further comprising a second pair of switching transistors, each connected to switch, in anti-phase to the other of the second pair of switching transistors, in response to the local oscillator signals, which second pair is connected to switch radio frequency signals present on a second terminal, common to the second pair, of the radio frequency input port of the mixer core, wherein one transistor of each of the first and second pairs is connected to switch, in anti-phase with the other of the one transistor of each of the first and second pairs, the radio frequency signals to a first terminal of the output port and the other transistor of each of the first and second pairs is connected to switch, in anti-phase with the other of the other transistor of each of the first and second pairs, the radio frequency signals to a second terminal of the output port, a DC detection circuit connected to receive the output of the mixer core and to provide a duty cycle adjustment control signal in response to the level of DC in the output of the mixer core, and a duty cycle control circuit having a local oscillator input port, an input port connected to receive the duty cycle adjustment control signal provided by the DC detection circuit, and an output port connected to apply local oscillator signals received on the local oscillator input port of the duty cycle control circuit to the local oscillator input port of the mixer core, wherein each local oscillator signal is applied to the mixer core via a different component consisting essentially of a capacitor to each input of the mixer core local oscillator input port, wherein the duty cycle control circuit is arranged so to apply the duty cycle adjustment control signal to the local oscillator signals as to change the duty cycle of the first pair of transistors of the mixer core relative to the duty cycle of the second pair of transistors of the mixer core.