Sensor Circuits - The Electronic Nose Artificial Olfaction Technology - page 182

List of analog circuits used as components of signal analysis/conditioning of
biosensors.

1. Conditioning bridge circuit
2. Amplifier for signal conditioning circuit

• Inverting amplifier
• Summing amplifier(extension of inverting)
• Non-inverting amplifier
• Differentiator
• Comparator
• Rectifier
• Integrator
3. Filter circuit

• Active
• Low pass
• High pass
• Band pass
4. ADC for signal conditioning circuit

1. Conditioning Bridge Circuit

Sensor outputs are often primarily in some non-voltage form; conversion to a
measurement signal that is in a more convenient form can be achieved by various
types of variable conversion elements in the measurement system. Bridge circuits
are a particularly important type of variable conversion elements. Bridge circuits
are among the basic fundamental and powerful electrical tools found in mea-
surement, switching, oscillator, and transducer circuits. Bridge circuit is an
accurate method of measuring resistance, inductance, and capacitance values, and
enables the detection of very small changes in these quantities of about a nominal
value.

at balance ;

R1
R1 þ R4

R2
R2 þ R3

V 0 ¼ 0if R1

R4 ¼ R2

V 0 ¼ V B

R3

Basically null and deflection types of bridge exist; null types are employed for
calibration purposes (balanced mode) and deflection types (unbalance mode) are
used within closed-loop automatic control schemes. Bridge is an attractive alter-
native to the potential divider.
A null-type bridge with d.c. excitation, commonly known as a Wheatstone
bridge, has the form shown in Fig. 7.3 . The bridge contains four resistors con-
nected to a quadrilateral, a source of excitation voltage defined as V B (or, alter-
nately, a current) connected across one of the diagonals of the bridge, and a
voltage detector connected across the other diagonal of bridge. The detector
measures the difference between the outputs of the two voltage dividers connected