Analog/differential circuits have numerous applications in varying areas of technologies. For example, differential amplifiers may be used in radio transmitters and receivers, in analog-to-digital converters, in semiconductor memory arrays, among numerous other applications. One application of such differential circuits that is becoming increasingly important is the area of single component (or semiconductor chip) radios, particularly those implementing direct conversion radio architectures. These direct conversion architectures, as is known, often implement a number of fully differential circuit stages. These fully differential circuit stages are typically sensitive to electrical noise. In this respect, any noise referred onto these signals is highly undesirable as each differential stage amplifies the signal (and noise) that it receives at its differential inputs.
In order to reduce the amount of noise referred, such differential signals are not typically referenced to ground and are “carried” on a common-mode voltage signal, which takes the form of a direct current (DC) voltage signal. This reduces the reference of electrical ground noise on to the differential signals. In the context of direct conversion radios, the common-mode voltages of different circuit stages are often quite different. In this regard, a radio frequency stage in such radio architectures may employ a different common mode voltage than a baseband stage. Such circuit stages are known to those working in this area and are not explained in detail here. In such applications, signals produced by circuit stages that have different common mode voltages are not compatible without first changing the common-mode voltage of one or more of the signals. In this regard, any such signals being processed by the same circuit stage typically have the same common-mode voltage. Adjusting such common-mode voltages is typically accomplished by employing a separate (additional) circuit stage to shift the common-mode voltage(s) of such signals.
Such an approach, however, has certain disadvantages. For example, such circuits typically convert differential signals being processed to single ended signals to accomplish such common-mode voltage shifts. These current approaches then typically use voltage follower circuits to apply such shifts. However, voltage follower circuits consume a relatively large amount of power (which is in addition to the noise created by the differential amplifier) and add noise to the signals being processed. Thus, such voltage follower circuits may degrade the quality of signal processing for circuits in which they are employed while consuming more power. Also, using a separate circuit stage to apply a common-mode voltage shift introduces additional circuit delay, which impacts the efficiency of circuits employing such techniques. Therefore, based on the foregoing, alternative approaches for applying a common-mode voltage shift are desirable.