High dynamic range radio architecture with enhanced image rejection
View Patent ↗A circuit for down-converting an RF signal to a baseband signal includes a trans-admittance amplifier adapted to receive the RF signal and generate in response a pair of differential current signals. The circuit further includes a trans-impedance amplifier having at least four mixers and at least four linear amplifiers. The four mixers frequency down-convert the pair of differential current signals to generate four pairs of differential baseband current signals, wherein each pair of the differential baseband current signals has a different phase and is associated with each of the linear amplifiers. Additionally, the circuit includes a summing block that generates an in-phase signal using a first weighted sum of the four different baseband current signals and a quadrature signal using a second weighted sum of the four different baseband current signals. The circuit further includes an analog-to-digital converter for converting the in-phase and quadrature signals to respective digital representations.
1. A circuit comprising:
a trans-admittance amplifier receiving a Radio Frequency (RF) signal and generating in response a pair of differential current signals;
a trans-impedance amplifier comprising at least four mixers and at least four amplifiers, the at least four mixers down-converting a frequency of the received pair of differential current signals to generate a first differential signal pair TZ 0 having a relative phase of 0 degrees, a second differential signal pair TZ 45 having a relative phase of 45 degrees, a third differential signal pair TZ 90 having a relative phase of 90 degrees, and a fourth differential signal pair TZ 135 having a relative phase of 135 degrees, each of the four pairs of differential signals having a phase corresponding to a different phase of a local oscillator signal, each of the at least four amplifiers being associated with a different one of the four pairs of differential signals; and
a summing block adapted to:
generate an in-phase signal using a first weighted sum of the four differential signals; and
generate a quadrature phase signal using a second weighted sum of the four differential signals, wherein the generated in-phase signal is defined substantially by
TZ 0 +(√2+1) TZ 45 +(√2+1) TZ 90 +TZ 135 .
2. The circuit of claim 1 , wherein the signal TZ 0 has a phase of 0 degrees relative to the phase of the local oscillator signal, wherein the signal TZ 45 has a phase of 45 degrees relative to the phase of the local oscillator signal, the signal TZ 90 has a phase of 90 degrees relative to the phase of the local oscillator signal, and wherein the signal TZ 135 has a phase of 135 degrees relative to the phase of the local oscillator signal.
3. The circuit of claim 2 , wherein each of the mixers receives a 12.5% duty cycle non-overlapping clock signal.
4. The circuit of claim 1 , wherein the generated quadrature signal is defined substantially by
(√2+1) TZ 0 +TZ 45 +TZ 90 +(√2+1) TZ 135 .
5. The circuit of claim 1 , wherein the trans-admittance amplifier comprises:
a low-noise amplifier having an input terminal and an output terminal;
a first gain stage having a first input capacitively coupled to the output terminal and a first output; and
a second gain stage having a second input capacitively coupled to the input terminal and a second output;
wherein a noise of the low-noise amplifier appearing at the first and second outputs are canceled by a common-mode rejection of the trans-impedance amplifier.
6. The circuit of claim 1 further comprising:
an analog-to-digital converter configured to convert the in-phase signal to a digital in-phase signal and the quadrature phase signal to a digital quadrature signal.
7. The circuit of claim 6 further comprising a processing unit configured to process the in-phase and quadrature digital signals.
8. A method for providing a baseband signal having reduced harmonics comprising:
receiving a Radio Frequency (RF) signal;
generating a pair of differential current signals in response to the received RF signal;
frequency down-converting the pair of differential current signals using at least four mixers to generate a first differential signal pair TZ 0 having a relative phase of 0 degrees, a second differential signal pair TZ 45 having a relative phase of 45 degrees, a third differential signal pair TZ 90 having a relative phase of 90 degrees, and a fourth differential signal pair TZ 135 having a relative phase of 135 degrees, each of the four pairs of differential signals having a different phase relative to a local oscillator signal;
generating an in-phase signal using a first weighted sum of the four pairs of differential signals; and
generating a quadrature signal using a second weighted sum of the four pairs of differential signals, wherein the generated in-phase signal is defined substantially by
TZ 0 +(√2+1) TZ 45 +(√2+1) TZ 90 +TZ 135 .
9. The method of claim 8 further comprising:
generating at least four different phases of the local oscillator signal; and
applying each of the at least four phases of the local oscillator signal to a different one of at least four mixers.
10. The method of claim 8 , wherein each of the at least four mixers receives a 12.5% duty cycle non-overlapping clock signal.
11. The method of claim 8 , wherein the generated quadrature phase signal is defined substantially by
(√2+1) TZ 0 +TZ 45 +TZ 90 +(√2+1) TZ 135 .