GP520A

Features:

• programmable parameters
- gain
- low pass filter
- high pass filter
- AGC threshold
- release time
- MPO
- receiver bias voltage
• on-chip voltage regulator
• typical gain 60 dB
• voltage drive output stage
• telecoil preamp


Pinout




Specifications

PARAMETER	VALUE / UNITS
Supply Voltage Pad 3, 8, 10, 11, 13, 17 Pad 1, 15, 16, 18, 19, 22, 24, 26 Pad 4, 5, 7, 14, 20, 21, 23, 25, 27 Pad 2	5 V -0.1 V to VCC + 0.1 V -0.1 V to VREG + 0.1 V -0.1 V to 0.7 V VREG -0.7 V to VREG + 0.1 V

Description

The GP520A is a programmable analog signal path IC designed for use in hearing instruments. The GP520A's programmable parameters are adjusted by external programming currents, such as generated by the GP521. The GP520A provides a 2.5 A reference current for use by the GP521. Sixteen settings are possible in the GP521, allowing the Programmable Current Sink (PCS) to sink between 0 and 1.875 x I_REF.

The GP520A is composed of five functional blocks. The input preamp, a filter block, the AGC block, MPO clipper and the output stage. Principle features of the preamp are the input impedance 100 k and a gain of 14 dB.

The programmable filter block of GP520A is composed of a low pass and high pass filter which generates a range of high and low pass corner frequencies. Although the control current to this block varies linearly, linear to logarithmic conversion is performed internally in order to adjust the corner frequencies logarithmically. Both filters feature a 12 dB/octave rolloff and unity gain.

The filters of GP520A are followed by an AGC block. Up to 35?dB of adjustable gain is provided as well as programmable threshold and release time. The attack time of the AGC block remains fixed and is independent of the release time. The output current is driven into the preamp of the clipper, thus, the AGC converts a voltage input into a current output and is therefore, a transconductance block.

The next stage of GP520A is an electronic MPO control peak "clipper" providing electronic clipping of the signal and setting of the maximum output level. The clipper output is also a transconductance block and drives a 40 k resistor (R_{OUT 8}) tied to the supply.

The input of the final stage is an inverting operational amplifier. A feedback resistance of 240 k is provided internally and this final stage is thus configured as a voltage drive output stage. The DC bias current through the receiver is also programmable.