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METHOD FOR GENERATION OF PROGRAMMABLE GAIN STEPS WITH CONSTANT BANDWIDTH

IP.com Disclosure Number: IPCOM000013985D
Original Publication Date: 2000-Feb-01
Included in the Prior Art Database: 2003-Jun-19
Document File: 5 page(s) / 112K

Publishing Venue

IBM

Abstract

Below is a larger diagram of the left ½ of the above circuit. 1 2 Below is the right ½ of the original circuit.

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  METHOD FOR GENERATION OF PROGRAMMABLE GAIN STEPS WITH CONSTANT BANDWIDTH

Below is a larger diagram of the left 1/2 of the above circuit.

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Below is the right 1/2 of the original circuit.

In many analog signal processing applications, there is a requirement to

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change the total gain of the system in discrete steps. In the past, this was
done with circuits that changed the collector or emitter resistor of an
amplifier using FET switches. One problem with this, for wide band
applications, is the effect the switches have on the upper 3 dB band point of
the amplifier. As the gain is changed, the 3 dB frequency will also change
because of the capacitance of the FET switches.

Disclosed below is a circuit that allows the gain to be changed without the
upper 3 dB frequency of the amplifier being changed.

Below are the major parts of the above circuit.
1. NPN transistors Q23, Q22, QBM, Q54, QT1, QT2, Q59, and QBP make up an
NPN current source system with a reference current input at pin ib and a
control input at pin PDN. These devices provide the current sinks for all of
the below gain and emitter follower stages.
2. NPN transistors Q11 and Q21 are emitter follower stages for the
differential input signal at input pins VIP and VIM. The output of these
emitter follower stages feed the inputs of the five gain stages described in 3
through 7 below.
3. NPN transistors Q1, Q2, resistors R123, R129, R162, R127, R165, R128,
and NFET transistors M124, M127 make up a gain stage with a gain of 12 dB.
4. NPN transistors Q119, Q120, resistors R121, R135, R162, R127, R165,
R128, and NFET transistors M91, M95 make up a gain stage with a gain of 9 dB.
5. NPN transistors Q88, Q95, resistors R103, R136, R162, R127, R165, R128,
and NFET transistors M92, M99 make up a gain stage with a gain of 6 dB.
6. NPN transistors Q89, Q97, resistors R104, R142, R162, R127, R165, R128,
and NFET transistors M93, M100 make up a gain stage with a gain of 3 dB.
7. NPN transistors Q90, Q98, resistors R107, R106, R162, R127, R165, R128,
and NFET transistors M94, M101 make up a gain stage...