US 6,807,406 B1Granted

Variable gain mixer circuit

AssigneeRF Micro Devices, Inc.

InventorsBehzad Razavi, Pengfei Zhang

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Abstract

In accordance with embodiments of the present invention, a receiver system is provided with a variable gain mixer circuit that is advantageous over current architectures used in wireless communication systems. The use of a variable gain mixer circuit simplifies the receiver architecture resulting in the elimination of additional circuit blocks and a reduction in complexity and cost. Moreover, one embodiment of the present invention includes a mixer circuit comprising a mixer core, a bias circuit coupled to the mixer core for providing a bias current, and a variable impedance network. The mixer core receives input signals and generates output currents that are coupled to the variable impedance network. Each of the output currents are selectively coupled to a voltage output node through a variable impedance. Variable gain is established by varying the impedance between the output currents of the mixer core and the voltage output node.

Claims28

Dependent claims

An apparatus including a receiver system, the receiver system comprising:

a first amplifier having an input coupled to receive an input RF signal and an output to produce an amplified RF signal;
a variable gain mixer circuit comprising:
a mixer core having a first input, a second input receiving the amplified RF signal, and a plurality of output currents;
a bias circuit coupled to the mixer core for providing a bias current;
and
a variable impedance network coupled to the plurality of output currents and having a variable impedance based on a digital control signal provided to a control input of the variable gain mixer, wherein each of the plurality of output currents is selectively coupled to a corresponding voltage output node through the variable impedance network;
a low pass filter coupled to the mixer output;
an analog-to-digital converter coupled to the low pass filter, the analog to digital converter producing a digital output signal;
and
a voltage controlled oscillator for producing an oscillator signal, the oscillator signal coupled to the first input of the variable gain mixer circuit;
wherein the variable gain mixer circuit receives the digital control signal at the control input for varying the gain of the mixer circuit.

8 more elements

An apparatus including a receiver system, the receiver system comprising:

a first amplifier having an input coupled to receive an input RF signal and an output to produce an amplified differential RF signal;
a variable gain mixer circuit comprising:
a differential input stage for receiving the amplified differential RF signal and generating first and second differential output currents;
a bias circuit having a bias output coupled to the differential input stage, the bias circuit receiving a bias signal, and in accordance therewith, generating a bias current at the bias output;
and
first and second variable impedance networks having corresponding first and second current input nodes, the first current input node coupled to the first differential output current and the second current input node coupled to the second differential output current, each variable impedance network including a digital input for receiving a digital control signal and a voltage output node;
wherein each current input node is selectively coupled to a plurality of network nodes in the corresponding variable impedance network in accordance with the digital control signal, and each network node having a unique impedance to the corresponding voltage output node;
a low pass filter coupled to each of the voltage output nodes of the variable gain mixer;
an analog-to-digital converter coupled to the low pass filter, the analog to digital converter producing a digital output signal;
and
a voltage controlled oscillator for producing an oscillator signal, the oscillator signal coupled to the first input of the variable gain mixer circuit;
wherein each of the variable impedance networks receives the digital control signal at the digital input for varying the gain of the variable gain mixer circuit.

9 more elements

An apparatus including a receiver system, the receiver system comprising:

A) a first amplifier having an input coupled to receive in input RF signal and an output to produce an amplified differential RF signal;
B) a variable gain mixer circuit comprising:
i) first and second transistors for receiving the amplified differential RF signal;
ii) a third transistor for receiving a modulated RF signal and for setting the DC bias current in the mixer;
and
iii) a variable impedance network having a first terminal coupled to the first supply voltage and a second terminal coupled to a first current output of at least one of the first and second transistors, the variable impedance network further comprising:
a) a plurality of network nodes;
b) a plurality of series resistors coupled between each of the network nodes each having a resistance R;
c) a plurality of shunt resistors coupled between the network nodes and the supply voltage each having a resistance of 2R;
d) a terminal shunt resistor coupled between a terminal network node and the supply voltage;
and
e) a plurality of switches for coupling the first current output to at least one of the network nodes based on a digital control signal;
C) a low pass filter coupled to one of the plurality of network nodes in the variable impedance network of the variable gain mixer;
D) an analog-to-digital converter coupled to the low pass filter, the analog to digital converter producing a digital output signal;
and
E) a voltage controlled oscillator for producing an oscillator signal, the oscillator signal coupled to the first input of the variable gain mixer circuit;
wherein the variable gain mixer circuit receives the digital control signal for varying the gain of the variable gain mixer circuit.

14 more elements

Dependencies are inferred from the claim text.