Linear Technology Corporation

Analog Devices,inc.

Analog Devices International Unlimited Company

Petrus Martinus Stroet

John Perry Myers

Apparatus and methods for logarithmic current to voltage conversion are disclosed herein. In certain embodiments, a logarithmic current to voltage converter includes an input terminal that receives an input current, an output terminal that provides a logarithmic output voltage, a first field-effect transistor (FET) having a gate connected to the input terminal, a first bipolar transistor having a collector connected to the input terminal and an emitter connected to the output terminal, and a stacked transistor connected to the output terminal and to the first FET to form a feedback loop. For example, the stacked transistor can correspond to a second bipolar transistor having a collector connected to the output terminal and a base connected to the source of the first FET, or to a second FET having a drain connected to the output terminal and a gate connected to the source of the first FET.

Logarithmic current to voltage converters

In a variable gain amplifier, a base of a bipolar first transistor receives a first differential input signal. The emitter of the first transistor is connected in series between a first resistor and a MOSFET coupled to ground. An output of the amplifier is a current through the collector. The conductivity of the MOSFET controls a gain of the amplifier. A bipolar second transistor receives a second differential input signal, and the second transistor provides a modulated gate voltage to the MOSFET. The drain voltage of the MOSFET is modulated by the first differential input signal and thus undesirably generates distortion. To reduce the distortion, the modulated gate voltage causes the AC component for a certain DC voltage at the drain of the MOSFET to be lowered, improving linearity. Since no current source is used, the amplifier has a large headroom, allowing operation using a low operating voltage.

Low-voltage analog variable gain amplifier with enhanced linearity

A tunable and trimmable analog filter may include a tunable analog filter and a trimming circuit. The tunable analog filter may set the frequency of a characteristic of the tunable analog filter based on a digital tuning signal that is indicative of a desired frequency of the characteristic. However, the tunable analog filter may contain components having values that deviate from specified values due to var during manufacture of the tunable analog filter. The value deviations can cause the frequency of the characteristic not to precisely match the frequency indicated by the digital tuning signal. The trimming circuit may include a non-volatile memory that contains data. The trimming circuit may receive tuning information indicative of a desired frequency for the characteristic of the tunable analog filter. The trimming circuit may generate the digital tuning signal by trimming the tuning information to compensate for the deviations in component value and by using the data contained within the non-volatile digital memory.

Exponential ROM table tuning using trim for frequency agile analog filters

A poly-phase filter receives inphase input signals I and &#x12a; and quadrature input signals Q and, and provides inphase output signals Iandand quadrature output signals Qand. The capacitance of each variable capacitor connected to the terminals providing inphase output signals Iandis and the capacitance of each variable capacitor connected to the terminals providing quadrature output signalsand Q, are different in value, and preferably by twice a predetermined value. This is because adjustment to the capacitance values may be made to each set of variable capacitors by the predetermined value.

Poly-phase filter with phase tuning

A single-balanced balun mixer circuit includes a balun with a center tap connected to a differential pair with a tail resistor. The balun receives a first input signal and a second signal at the single-ended input terminal and the center tap, respectively. Such a balun mixer may be used as an up-converter mixer by supplying a baseband or intermediate signal at the center tap and a local oscillator (LO) signal at the single-ended input terminal.

Balun mixer circuits

A mixer in an RF demodulator includes a transconductance amplifier that converts an RF input voltage (Vin), applied to the base of a first bipolar transistor, to a first output current. The first output current contains third order intermodulation (IM3) products. An IM3 canceller is connected in parallel with the transconductance amplifier. The base of a second bipolar transistor in the IM3 canceller is coupled to the DC component of Vin, and the AC component of Vin is coupled to the emitter of the second bipolar transistor, such that the currents though the first bipolar transistor and the currents through the second bipolar transistor change oppositely. The collectors of the transistors are coupled together. The values of components in the IM3 canceller are set so that the current generated by the IM3 canceller substantially cancels IM3 distortion in the first current or other current generated in a demodulator of Vin.

Third order intermodulation cancellation for RF transconductors

Circuits and methods for a low voltage pre-distortion circuits that provide a temperature and logarithmically compensated voltage such that a gain change of a variable gain amplifier is linear in dB and has a reduced temperature dependency. A temperature compensation circuit multiplies the transfer function of gain of the amplifier versus gain control voltage by absolute temperature. A logarithmic compensation circuit removes the non-logarithmic factor of a '1' in the denominator of the transfer function.

Low-voltage pre-distortion circuit for linear-in-dB variable-gain cells

Circuits and methods for providing a variable gain while powered from a low-voltage supply. In a specific embodiment, an input signal is converted to a current by an emitter-degenerated pair. A portion of the input current is discarded, while the remainder is variably steered between a shunt stage or an AC ground such as VCC. The output of the shunt stage is buffered by a high speed output, the bandwidth of which is increased by feed-forward capacitors. This arrangement may be optionally repeated for additional gain.

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Santa Cruz, CA, United States of America

Petrus Martinus Stroet