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mm-Waves Down-conversion Mixer, Bandpass filter and Variable Gain Amplifier (VGA)

IP.com Disclosure Number: IPCOM000234037D
Publication Date: 2014-Jan-08
Document File: 3 page(s) / 2M

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a single balanced mixer with a tunable bandpass filter (BPF) at the output for sliding Intermediate Frequency (IF) architecture.

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mm

mm- ( (VGA

VGA)

For superheterodyne (superhet) receivers, the output of the first mixer is filtered out

with a bandpass filter (BPF) before Intermediate Frequency (IF) amplification. Apart

from conversion gain and low noise figure, the mixer load should have a frequency tuning mechanism independent from the quality factor of the filter . When the Radio Frequency (RF) input signal is single ended, a single balanced mixer is a possible choice. However, a strong Local Oscillator (LO) component is present at the output (at LO frequency). This component is not well filtered at the output of the mixer and saturates the next stages.

Current solutions involve a current leaker resistor or a current source taking away part of the current from the switching stage. By this, the switching transistors can be small and the LO driver can be scaled down in power. However, this can increase the parasitic capacitance at the sources of the switching stage .

The present solution is a single balanced mixer with a tunable BPF at the output for sliding IF architecture. The frequency tuning and Q tuning are decoupled from each other. Changing the Q factor alters the gain of the mixer without affecting the linearity of the Variable Gain Amplifier (VGA). There is no need for buffers as impedance transformers between VGA stage and the mixer. The under stage is biased at large currents for low noise and high linearity. A shorted stub resonates the capacitance at the output of the under stage, boosting the gain of the mixer. The leaker Digital Analog Converter (DAC) current is applied at the shorted output of the stub . This filters out its noise and its parasitic capacitance does not load the switching stage node .

Figure 1: Down Conversion Mixer Core

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