S. Jantzi

A fourth-order bandpass sigma-delta modulator

The modulator of a bandpass analog/digital (A/D) converter, with 63 dB signal/noise for broadcast AM bandwidth signals centered at 455 kHz, has been implemented by modifying a commercial digital-audio sigma-delta ( Sigma Delta ) converter. It is the first reported fully monolithic implementation of bandpass noise shaping and has applications to digital radio. >

BALLISTIC: an analog layout language

A high-level language intended for analog layout is described. Code written in the language is compiled into the Mentor Graphics Lx language and executed in the GDT layout environment. The language allows analog circuits to be described hierarchically using objects such as transistors, differential-pairs, current-mirrors, and capacitor arrays as building-blocks (custom library objects are also supported). All objects are fully-parameterized and technology-independent, and placement and routing are specified relatively. Hence, circuits described in the language are easily ported to new technologies without changing code. The language is also concise. For example, a fully-parameterized op amp was described using 230 lines of BALLISTIC code, as compared to over 17,000 lines of Lx code.

A complex bandpass /spl Delta//spl Sigma/ converter for digital radio

A new architecture is proposed for a single-chip digital radio receiver. This architecture has several advantages over the direct-conversion architecture that has been gaining interest for use in single-chip designs. A non-zero quadrature IF reduces the image problem and eliminates concerns about self-EMI and 1/f noise. A complex bandpass filter embedded in a delta-sigma loop allows the A/D conversion to be performed directly on the pair of quadrature outputs from the mixer.<<ETX>>

The effects of mismatch in complex bandpass /spl Delta//spl Sigma/ modulators

Mismatch between the real and imaginary channels of a complex system is examined and equations are presented that show the relationship between mismatch and image rejection. An example is given that demonstrates the effects of mismatch on the properties of a complex filter. These results are applied to the design of a fourth-order complex bandpass /spl Delta//spl Sigma/ modulator and a technique is discussed that alleviates the negative effects of mismatch on modulator performance. The technique modifies a modulators noise transfer function by placing a notch in its image band, giving an SNR performance improvement of approximately 15 dB (2.5 bits) over an unmodified modulator. The practical implementation of this technique is discussed.

Transfer function design for /spl Delta//spl Sigma/ converters

A methodology is presented for the design of noise and signal transfer functions for delta-sigma modulators. A computerised optimiser is used to produce maximal noise-shaping, while meeting those constraints necessary to realise a usable modulator. The design of higher-order modulators is possible, as is the design of unique noise-shaping functions such as for bandpass modulators, complex modulators, or modulators with psychoacoustically-shaped in-band noise. Optimisation of the transfer function from modulator input to output is also possible if special conditioning of the input signal is desired.<<ETX>>