Design Using Op Amp

[compudel]

I am looking for a good circuit design analysis online of a Voltage-controlled current source (vccs) and a bridge amplifier using op-amps.<p>The vccs would be in the configuration of a feedback resistor and an input resistor that is referenced to ground, with their intersection wired to the inverting input. A similar feedback resistor and an input resistor that is also referenced to ground, with their intersection tied to the non-inverting input. Also on the non-inverting input is the input dc voltage source wired to a current limiting resistor, which is also wired to the non-inverting input.
For the bridge amplifier circuit, a dc voltage source is shunted between the legs of the bridge resistors. At the intersection of the resistors on one leg, it is wired to the inverting input; and, at the intersecton of the resistors on the other leg, it is wired to the intersection of a pull-up resistor on the output of the op-amp and a pull-down resistor wired to ground. The non-inverting input is also wired to ground.
I know this is a mouth full, but a simple sketch of the two (2) circuits will simplify the wording.<p>Thanks for any feedback,
Robert

[russlk]

Neither of the circuits makes any sense. Where is the output of the VCCS? Certainly not at the op amp output.<p>You cannot make a bridge amplifier using one op amp. There are numerous examples on the web.<p>I can design a VCCS using 3 op amps if you are interested.

[compudel]

Russ, I appreciate your reply, and please forgive me for not responding earlier. I was able to find the circuit in an Electrical Engineering textbook. The circuit is known as a "Howland" current source. It is actually a Voltage Controlled Current Source. In fact, I was able to discover it was covered as a teaser in one of my technical publications-"Circuit Cellar." It was in the October, 2004 issue. The solution is posted on the Circuit Cellar bulletin board. The feedback resistors and input resistors on both sides of the single op-amp is what creates the balanced bridge concept. Mr. Knowland, I assume, was the first individual to document the behavior of this circuit. If you go to the web site, I will assure you there is but one op-amp.
For the second circuit, the analysis of the Bridge amplifier was just an oversight on my part. Once I viewed the circuit and proceeded through the fundamentals, I was able to derive the output equation.
Again thanks for the feedback.
Robert